Lennox International Inc Furnace DAVE LENNOX SIGNATURE COLLECTION GAS FURNACE UPFLOW HORIZONTAL AIR DISCHARGE User Manual
INSTALLATION  
INSTRUCTIONS  
SL280UHV  
E 2011 Lennox Industries Inc.  
Dallas, Texas, USA  
®
DAVE LENNOX SIGNATURE  
COLLECTION GAS FURNACE  
UPFLOW / HORIZONTAL AIR DISCHARGE  
506763−01  
06/2011  
Supersedes 03/2011  
Litho U.S.A.  
THIS MANUAL MUST BE LEFT WITH THE  
HOMEOWNER FOR FUTURE REFERENCE  
This a safety alert symbol and should never be ignored.  
When you see this symbol on labels or in manuals, be alert  
to the potential for personal injury or death.  
CAUTION  
UPFLOW  
As with any mechanical equipment, personal injury  
can result from contact with sharp sheet metal  
edges. Be careful when you handle this equipment.  
AIR FLOW  
NOTICE  
A thermostat is not included and must be ordered  
separately.  
®
AIR FLOW  
AIR FLOW  
D The Lennox icomfort Touch thermostat must be  
used in communicating applications.  
HORIZONTAL LEFT  
HORIZONTAL RIGHT  
D In non−communicating applications, the Lennox  
®
ComfortSense 7000 thermostat may be used, as  
well as other non−communicating thermostats.  
WARNING  
In all cases, setup is critical to ensure proper sys-  
tem operation.  
Improper installation, adjustment, alteration, service  
or maintenance can cause property damage, person-  
al injury or loss of life. Installation and service must  
be performed by a licensed professional installer (or  
equivalent), service agency or the gas supplier.  
Field wiring for both communicating and non−com-  
municating applications is illustrated in diagrams,  
which begin on Page 27.  
Table of Contents  
Unit Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2  
Parts Arrangement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3  
SL280UHV Gas Furnace . . . . . . . . . . . . . . . . . . . . . . . . . 4  
Shipping and Packing List . . . . . . . . . . . . . . . . . . . . . . . . 4  
Safety Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4  
Use of Furnace as a Construction Heater . . . . . . . . . . . 5  
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5  
Combustion, Dilution & Ventilation Air . . . . . . . . . . . . . . 6  
Electrical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25  
Integrated Control Settings . . . . . . . . . . . . . . . . . . . . . . . 36  
Blower Performance Data . . . . . . . . . . . . . . . . . . . . . . . . 39  
Unit Start−Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51  
Gas Pressure Adjustment . . . . . . . . . . . . . . . . . . . . . . . . 52  
Proper Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52  
High Altitude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53  
Other Unit Adjustments . . . . . . . . . . . . . . . . . . . . . . . . . . 54  
Heating Sequence of Operation . . . . . . . . . . . . . . . . . . . 54  
Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56  
Planned Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59  
Repair Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59  
Integrated Control Diagnostic Codes . . . . . . . . . . . . . . . 60  
Program Unit Capacity/Size Mode . . . . . . . . . . . . . . . . . 67  
Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68  
Setting Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9  
Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12  
Duct System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12  
Venting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13  
Gas Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23  
06/11  
506763−01  
Page 1  
*2P0611*  
*P506763-01*  
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Parts Arrangement  
HEAT EXCHANGER  
COMBUSTION AIR INDUCER  
COMBUSTION AIR INDUCER  
PRESSURE SWITCH  
GAS VALVE  
CABINET  
ROLLOUT SWITCH  
BURNER BOX  
INNER BLOWER  
ACCESS PANEL  
CONTROL BOX  
(Includes two−stage integrated control,  
transformer and circuit breaker)  
SIGHT GLASS  
ACCESS PANEL  
BLOWER  
ASSEMBLY  
FIGURE 1  
Page 3  
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SL280UHV Gas Furnace  
WARNING  
Improper installation, adjustment, alteration, service  
or maintenance can cause property damage, person-  
al injury or loss of life. Installation and service must  
be performed by a licensed professional installer (or  
equivalent), service agency or the gas supplier.  
The SL280UHV gas furnace is equipped with a two−stage,  
variable speed integrated control. the control is compat-  
ible with:  
®
Communicating thermostats − icomfort Touch .  
Non−comunicating thermostats − ComfortSense or other  
conventional thermostats.  
Control systems − Harmony IIIꢀ Zone Control System  
(non−communicating).  
CAUTION  
Each SL280UHV unit is shipped ready for installation in  
the upflow or horizontal position (left or right). The furnace  
is shipped with the bottom panel in place. The bottom pan-  
el must be removed if the unit is to be installed in a horizon-  
tal application. The panel may also be removed in upflow  
applications.  
As with any mechanical equipment, personal injury  
can result from contact with sharp sheet metal  
edges. Be careful when you handle this equipment.  
Certifications  
SL280UHV units are CSA International certified to ANSI  
Z21.47.  
In the USA, installation of gas furnaces must conform with  
local building codes. In the absence of local codes, units  
must be installed according to the current National Fuel  
Gas Code (ANSI-Z223.1). The National Fuel Gas Code is  
available from the following address:  
Shipping and Packing List  
Package 1 of 1 contains  
1 − Assembled SL280UHV unit  
1 − Bag assembly containing the following:  
2 −Screws  
American National Standards Institute, Inc.  
11 West 42nd Street  
New York, NY 10036  
1 −Snap bushing  
Clearances  
1 −Snap plug  
Adequate clearance must be made around the air open-  
ings into the vestibule area. In order to ensure proper unit  
operation, combustion and ventilation air supply must be  
provided according to the current National Fuel Gas Code.  
1 − Wire tie  
1 −Vent warning label  
1 −Owner’s manual and warranty card  
The following items may be ordered separately:  
1 − Thermostat  
Vent installations must be consistent with the venting  
tables (in this instruction) and applicable provisions of local  
building codes.  
1 − Suspension Kit (for horizontal installations)  
1 − Propane/LP changeover kit  
1 − Return air base  
This furnace is CSA International certified for installation  
clearances to combustible material as listed on the unit  
nameplate and in the tables in figures 7 and 11. Accessibility  
and service clearances must take precedence over fire  
protection clearances.  
1 − High altitude kit  
1 − Side filter kit  
Check equipment for shipping damage. If you find any  
damage, immediately contact the last carrier.  
NOTE − For installation on combustible floors, the furnace  
shall not be installed directly on carpeting, tile, or other  
combustible material other than wood flooring.  
Safety Information  
Installed Locations  
For installation in a residential garage, the furnace must  
be installed so that the burner(s) and the ignition source  
are located no less than 18 inches (457 mm) above the  
floor. The furnace must be located or protected to avoid  
physical damage by vehicles. When a furnace is installed  
in apublic garage, hangar, or other building that has a haz-  
ardous atmosphere, the furnace must be installed accord-  
ing to recommended good practice requirements and cur-  
rent National Fuel Gas Code.  
DANGER  
Danger of explosion.  
There are circumstances in which odorant used with  
LP/propane gas can lose its scent. In case of a leak,  
LP/propane gas will settle close to the floor and may  
be difficult to smell. An LP/propane leak detector  
should be installed in all LP applications.  
Page 4  
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Temperature Rise  
The SL280UHV furnace may be installed in alcoves, clos-  
ets, attics, basements, garages, and utility rooms in the up-  
flow or horizontal position.  
NOTE − Furnace must be adjusted to obtain a temperature  
rise(high and low fire) within the range(s) specified on the unit  
nameplate. Failure to do so may cause erratic limit operation  
and may result in premature heat exchanger failure.  
This furnace is not designed for installation in mobile  
homes, recreational vehicles, or outdoors.  
Never use an open flame to test for gas leaks. Check all  
connections using a commercially available soap solution  
made specifically for leak detection.  
This SL280UHV furnace must be installed so that its elec-  
trical components are protected from water.  
Installed in Combination with a Cooling Coil  
Use of Furnace as Construction Heater  
When this furnace is used with cooling units, it shall be  
installed in parallel with, or on the upstream side of, cooling  
units to avoid condensation in the heating compartment.  
See figure 1. With a parallel flow arrangement, a damper (or  
other means to control the flow of air) must adequately pre-  
vent chilled air from entering the furnace. If the damper is  
manually operated, it must be equipped to prevent operation  
of either the heating or the cooling unit, unless it is in the full  
HEAT or COOL setting. See figure 1.  
Lennox does not recommend the use of SL280UHV units  
as a construction heater during any phase of construction.  
Very low return air temperatures, harmful vapors and op-  
eration of the unit with clogged or misplaced filters will dam-  
age the unit.  
SL280UHV units may be used for heating of buildings or  
structures under construction, if the following conditions  
are met:  
D The vent system must be permanently installed per  
these installation instructions.  
Heating Unit Installed Parallell to Air Handler Unit  
Dampers  
(open during heating operation only)  
D A room thermostat must control the furnace. The use of  
fixed jumpers that will provide continuous heating is not  
allowed.  
Gas Unit  
D The return air duct must be provided and sealed to the  
furnace.  
D Return air temperature range between 60°F (16°C) and  
80°F (27°C) must be maintained.  
Air Handler Unit  
D Air filters must be installed in the system and must be  
maintained during construction.  
Dampers  
(open during cooling operation only)  
D Air filters must be replaced upon construction comple-  
tion.  
D The input rate and temperature rise must be set per the  
furnace rating plate.  
Heating Unit Installed Upstream of Cooling Unit  
D One hundred percent (100%) outdoor air must be pro-  
vided for combustion air requirements during construc-  
tion. Temporary ducting may supply outdoor air to the  
furnace. Do not connect duct directly to the furnace.  
Size the temporary duct following these instructions in  
section for Combustion, Dilution and Ventilation Air in a  
confined space with air from outside.  
Gas Unit  
Evaporator  
FIGURE 1  
When installed, this furnace must be electrically grounded  
according to local codes. In addition, in the United States,  
installation must conform with the current National Elec-  
tric Code, ANSI/NFPA No. 70. The National Electric Code  
(ANSI/NFPA No. 70) is available from the following ad-  
dress:  
D The furnace heat exchanger, components, duct system,  
air filters and evaporator coils must be thoroughly  
cleaned following final construction clean−up.  
D All furnace operating conditions (including ignition, in-  
put rate, temperature rise and venting) must be verified  
according to these installation instructions.  
National Fire Protection Association  
1 Battery March Park  
General  
Quincy, MA 02269  
These instructions are intended as a general guide and do  
not supersede local codes in any way. Consult authorities  
having jurisdiction before installation.  
NOTE − This furnace is designed for a minimum continu-  
ous return air temperature of 60°F (16°C) or an intermit-  
tent operation down to 55°F (13°C) dry bulb for cases  
where a night setback thermostat is used. Return air tem-  
perature must not exceed 85°F (29°C) dry bulb.  
In addition to the requirements outlined previously, the fol-  
lowing general recommendations must be considered  
when installing a SL280UHV furnace:  
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D Place the furnace as close to the center of the air dis-  
tribution system as possible. The furnace should also be  
located close to the chimney or vent termination point.  
needs and requirements for exhaust vents and gas piping.  
A portion of this information has been reprinted with per-  
mission from the National Fuel Gas Code (ANSI-Z223.1).  
This reprinted material is not the complete and official posi-  
tion of the ANSI on the referenced subject, which is repre-  
sented only by the standard in its entirety.  
D Do not install the furnace where drafts might blow direct-  
ly into it. This could cause improper combustion and un-  
safe operation.  
D Do not block the furnace combustion air openings with  
clothing, boxes, doors, etc. Air is needed for proper  
combustion and safe unit operation.  
CAUTION  
Do not install the furnace in a corrosive or contami-  
nated atmosphere. Meet all combustion and ventila-  
tion air requirements, as well as all local codes.  
D When the furnace is installed in an attic or other insu-  
lated space, keep insulation away from the furnace.  
NOTE − The Commonwealth of Massachusetts stipu-  
lates these additional requirements:  
D Gas furnaces shall be installed by a licensed plumb-  
er or fitter only.  
CAUTION  
D The gas cock must be ꢀT handle" type.  
Insufficient combustion air can cause headaches,  
nausea, dizziness or asphyxiation. It will also cause  
excess water in the heat exchanger resulting in rust-  
ing and premature heat exchanger failure. Excessive  
exposure to contaminated combustion air will result  
in safety and performance related problems. Avoid  
exposure to the following substances in the combus-  
tion air supply:  
D When a furnace is installed in an attic, the passage-  
way to and service area surrounding the equipment  
shall be floored.  
WARNING  
Product contains fiberglass wool.  
Permanent wave solutions  
Chlorinated waxes and cleaners  
Chlorine base swimming pool chemicals  
Water softening chemicals  
De-icing salts or chemicals  
Carbon tetrachloride  
Halogen type refrigerants  
Cleaning solvents (such as perchloroethylene)  
Printing inks, paint removers, varnishes, etc.  
Hydrochloric acid  
Disturbing the insulation in this product during  
installation, maintenance, or repair will expose you  
to fiberglass wool. Breathing this may cause lung  
cancer. (Fiberglass wool is known to the State of Cal-  
ifornia to cause cancer.)  
Fiberglass wool may also cause respiratory, skin,  
and eye irritation.  
To reduce exposure to this substance or for further  
information, consult material safety data sheets  
available from address shown below, or contact your  
supervisor.  
Cements and glues  
Antistatic fabric softeners for clothes dryers  
Masonry acid washing materials  
Lennox Industries Inc.  
P.O. Box 799900  
Dallas, TX 75379−9900  
All gas-fired appliances require air for the combustion pro-  
cess. If sufficient combustion air is not available, the fur-  
nace or other appliances will operate inefficiently and un-  
safely. Enough air must be provided to meet the needs of all  
fuel-burning appliances and appliances such as exhaust  
fans which force air out of the house. When fireplaces, ex-  
haust fans, or clothes dryers are used at the same time as  
the furnace, much more air is necessary to ensure proper  
combustion and to prevent a downdraft. Insufficient air  
causes incomplete combustion which can result in carbon  
monoxide.  
Combustion, Dilution & Ventilation Air  
In the past, there was no problem in bringing in sufficient out-  
door air for combustion. Infiltration provided all the air that  
was needed. In today’s homes, tight construction practices  
make it necessary to bring in air from outside for combus-  
tion. Take into account that exhaust fans, appliance vents,  
chimneys, and fireplaces force additional air that could be  
used for combustion out of the house. Unless outside air is  
brought into the house for combustion, negative pressure  
(outside pressure is greater than inside pressure) will build  
to the point that a downdraft can occur in the furnace vent  
pipe or chimney. As a result, combustion gases enter the liv-  
ing space creating a potentially dangerous situation.  
In addition to providing combustion air, fresh outdoor air  
dilutes contaminants in the indoor air. These contami-  
nants may include bleaches, adhesives, detergents, sol-  
vents and other contaminants which can corrode furnace  
components.  
In the absence of local codes concerning air for combus-  
tion and ventilation, use the guidelines and procedures in  
this section to install SL280UHV furnaces to ensure effi-  
cient and safe operation. You must consider combustion air  
The requirements for providing air for combustion and ven-  
tilation depend largely on whether the furnace is installed in  
an unconfined or a confined space.  
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Unconfined Space  
Air from Inside  
An unconfined space is an area such as a basement or  
large equipment room with a volume greater than 50 cubic  
If the confined space that houses the furnace adjoins a  
space categorized as unconfined, air can be brought in by  
providing two permanent openings between the two  
spaces. Each opening must have a minimum free area of 1  
3
feet (1.42 m ) per 1,000 Btu (.29 kW) per hour of the com-  
bined input rating of all appliances installed in that space.  
This space also includes adjacent rooms which are not  
separated by a door. Though an area may appear to be un-  
confined, it might be necessary to bring in outdoor air for  
combustion if the structure does not provide enough air by  
infiltration. If the furnace is located in a building of tight  
construction with weather stripping and caulking around  
the windows and doors, follow the procedures in the air  
from outside section.  
2
square inch (645 mm ) per 1,000 Btu (.29 kW) per hour of  
total input rating of all gas−fired equipment in the confined  
space. Each opening must be at least 100 square inches  
2
(64516 mm ). One opening shall be within 12 inches (305  
mm) of the top of the enclosure and one opening within 12  
inches (305 mm) of the bottom. See figure 2.  
Air from Outside  
If air from outside is brought in for combustion and ventila-  
tion, the confined space must have two permanent open-  
ings. One opening shall be within 12 inches (305 mm) of the  
top of the enclosure and one opening within 12 inches (305  
mm) of the bottom. These openings must communicate di-  
rectly or by ducts with the outdoors or spaces (crawl or at-  
tic) that freely communicate with the outdoors or indirectly  
through vertical ducts. Each opening shall have a minimum  
Confined Space  
A confined space is an area with a volume less than 50 cu-  
3
bic feet (1.42 m ) per 1,000 Btu (.29 kW) per hour of the  
combined input rating of all appliances installed in that  
space. This definition includes furnace closets or small  
equipment rooms.  
When the furnace is installed so that supply ducts carry air  
circulated by the furnace to areas outside the space contain-  
ing the furnace, the return air must be handled by ducts  
which are sealed to the furnace casing and which terminate  
outside the space containing the furnace. This is especially  
important when the furnace is mounted on a platform in a  
confined space such as a closet or small equipment room.  
Even a small leak around the base of the unit at the platform  
or at the return air duct connection can cause a potentially  
dangerous negative pressure condition. Air for combustion  
and ventilation can be brought into the confined space either  
from inside the building or from outside.  
2
free area of 1 square inch (645 mm ) per 4,000 Btu (1.17  
kW) per hour of total input rating of all equipment in the en-  
closure. See figures 3 and 4. When communicating with  
the outdoors through horizontal ducts, each opening shall  
2
have a minimum free area of 1 square inch (645 mm ) per  
2,000 Btu (.56 kW) per total input rating of all equipment in  
the enclosure. See figure 5.  
When ducts are used, they shall be of the same cross−sec-  
tional area as the free area of the openings to which they  
connect. The minimum dimension of rectangular air ducts  
shall be no less than 3 inches (75 mm). In calculating free  
area, the blocking effect of louvers, grilles, or screens must  
be considered. If the design and free area of protective cov-  
ering is not known for calculating the size opening required,  
it may be assumed that wood louvers will have 20 to 25 per-  
cent free area and metal louvers and grilles will have 60 to  
75 percent free area. Louvers and grilles must be fixed in the  
open position or interlocked with the equipment so that they  
are opened automatically during equipment operation.  
EQUIPMENT IN CONFINED  
SPACE ALL AIR FROM INSIDE  
CHIMNEY  
OR GAS  
VENT  
WATER  
HEATER  
FURNACE  
OPENINGS  
(To Adjacent  
Room)  
AIR FLOW  
NOTE − Each opening shall have a free area of at least one square  
2
inch (645 mm ) per 1,000 Btu (.29 kW) per hour of the total input rat-  
ing of all equipment in the enclosure, but not less than 100 square  
2
inches (64516 mm ).  
FIGURE 2  
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EQUIPMENT IN CONFINED SPACE  
ALL AIR FROM OUTSIDE  
(Inlet Air from Crawlspace and Outlet Air to Ventilated Attic)  
CHIMNEY OR  
GAS VENT  
VENTILATION LOUVERS  
(Each end of attic)  
OUTLET  
AIR  
WATER  
HEATER  
FURNACE  
INLET  
AIR  
VENTILATION  
LOUVERS  
(For unheated crawl space)  
AIR FLOW  
NOTE−The inlet and outlet air openings shall each have a free area of at least one square inch (645  
2
mm ) per 4,000 Btu (1.17 kW) per hour of the total input rating of all equipment in the enclosure.  
FIGURE 3  
EQUIPMENT IN  
CONFINED SPACE  
ALL AIR FROM  
OUTSIDE  
EQUIPMENT IN CONFINED SPACE  
ALL AIR FROM OUTSIDE  
(All Air Through Ventilated Attic)  
CHIMNEY  
OR GAS  
VENT  
CHIMNEY  
OR GAS  
VENT  
WATER  
HEATER  
VENTILATION LOUVERS  
(Each end of attic)  
OUTLET AIR  
OUTLET  
AIR  
FURNACE  
FURNACE  
INLET AIR  
(Ends 12 in.  
above bottom)  
INLET AIR  
AIR FLOW  
WATER  
HEATER  
AIR FLOW  
NOTE − Each air duct opening shall have a free area of at least  
2
one square inch (645 mm ) per 2,000 Btu (.59 kW) per hour of  
the total input rating of all equipment in the enclosure. If the  
equipment room is located against an outside wall and the air  
openings communicate directly with the outdoors, each open-  
ing shall have a free area of at least one square inch (645 mm )  
per 4,000 Btu (1.17 kW) per hour of the total input rating of all  
other equipment in the enclosure.  
NOTE−The inlet and outlet air openings shall each have a  
2
free area of at least one square inch (645 mm ) per 4,000  
Btu (1.17 kW) per hour of the total input rating of all equip-  
ment in the enclosure.  
2
FIGURE 4  
FIGURE 5  
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Upflow Applications  
Setting Equipment  
Allow for clearances to combustible materials as indicated  
on the unit nameplate. Minimum clearances for closet or al-  
cove installations are shown in figure 7.  
WARNING  
Do not install the furnace on its front or its back. Do  
not connect the return air ducts to the back of the fur-  
nace. Doing so will adversely affect the operation of  
the safety control devices, which could result in per-  
sonal injury or death.  
Upflow Application Installation Clearances  
Top  
The SL280UHV gas furnace can be installed as shipped  
in either the upflow position or the horizontal position.  
Select a location that allows for the required clearances  
that are listed on the unit nameplate. Also consider gas  
supply connections, electrical supply, vent connection,  
and installation and service clearances [24 inches (610  
mm) at unit front]. The unit must be level.  
Left Side  
Right Side  
AIR FLOW  
NOTE − Units with 1/2 hp blower motors are equipped with  
three flexible legs and one rigid leg. See figure 6. The rigid  
leg is equipped with a shipping bolt and a flat white plastic  
washer (rather than the rubber mounting grommet used  
with a flexible mounting leg). The bolt and washer must  
be removed before the furnace is placed into opera-  
tion. After the bolt and washer have been removed, the rig-  
id leg will not touch the blower housing.  
Bottom  
Type of Vent  
Connector  
Type C  
Type B1  
Top  
*Front  
Back  
Sides  
Vent  
1 in. (25 mm)  
1 in. (25 mm)  
2−1/4 in. (57 mm)**  
2−1/4 in. (57 mm)  
0
0
0†  
6 in. (152 mm)  
0‡  
0
1 in. (25 mm)  
0‡  
SL280UHV07036A and  
SL280UHV09036B WITH 1/2 HP  
BLOWER MOTOR  
Floor  
*Front clearance in alcove installation must be 24 in. (610 mm).  
Maintain a minimum of 24 in. (610 mm) for front service access.  
** 3−1/4 in. if single wall vent pipe is used.  
‡For installation on a combustible floor, do not install the furnace  
directly on carpeting, tile or other combustible materials other  
than wood flooring.  
RIGID LEG  
remove shipping bolt and washer  
†Left side requires 3 inches if a single wall vent is used on 14−1/2  
inch cabinets, or 2 in. if a single wall vent is used on 17−1/2 in. cabi-  
nets.  
FIGURE 7  
FIGURE 6  
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Return Air −− Upflow Applications  
Single Side Return Air  
(with transition and filter)  
Return air can be brought in through the bottom or either  
side of the furnace installed in an upflow application. If the  
furnace is installed on a platform with bottom return, make  
an airtight seal between the bottom of the furnace and the  
platform to ensure that the furnace operates properly and  
safely. The furnace is equipped with a removable bottom  
panel to facilitate installation.  
20” X 25” X 1”  
(508mm X635mm X 25mm)  
Cleanable Filter  
Markings are provided on both sides of the furnace cabinet  
for installations that require side return air. Cut the furnace  
cabinet at the maximum dimensions shown on page 2.  
NOTE −60C and 60D units that require air volumes over 1800  
cfm (850 L/s) must have one of the following:  
Return Air  
Plenum  
1 − Return air from single side with transition which will  
accommodate 20 x 25 x 1 in. (508 x 635 x 25 mm) clean-  
able air filter. (Required to maintain proper air velocity.)  
See figure 8.  
AIR FLOW  
2 − Return air from single side with optional RAB Return  
Air Base. See figure 9.  
Transition  
3 − Return air from bottom and one side.  
4 − Return air from both sides.  
5 − Return air from bottom.  
FIGURE 8  
Refer to Engineering Handbook for additional information.  
Optional Return Air Base  
(Upflow Applications Only −− For use with A, B, C and D cabinets)  
FURNACE  
FRONT  
1 23 (584)  
IF BASE  
3−1/4  
(83)  
IS USED  
WITHOUT  
IAQ CABINET,  
A SINGLE  
RETURN AIR  
PLENUM  
Overall  
1 Minimum  
11 (279)  
(Maximum)  
INDOOR AIR  
2
1 22−7/16  
(570)  
Maximum  
1 Unit side return air  
Opening  
14 (356)  
Overall  
MUST  
AIR FLOW  
(Maximum)  
COVER BOTH  
UNIT AND  
RETURN  
AIR BASE  
OPENINGS  
SIDE RETURN  
5−5/8  
(143)  
7−1/4  
(184)  
AIR OPENINGS  
(Either Side)  
23  
3/4  
(19)  
OPTIONAL  
RETURN AIR BASE  
(584)  
26−7/8  
14−1/2” (368) A Width (65W75)  
17−1/2” (446) B Width (50W98)  
21”− (533) C Width (50W99)  
(683)  
SIDE VIEW  
24−1/2”− (622) D Width (51W00)  
NOTE− Optional Side Return Air Filter Kits are not for use with Optional Return Air Base.  
1
Both the unit return air opening and the base return air opening must be covered by a single plenum or IAQ cabinet.  
Minimum unit side return air opening dimensions for units requiring 1800 cfm or more of air (W x H): 23 x 11 in. (584 x 279 mm).  
The opening can be cut as needed to accommodate plenum or IAQ cabinet while maintaining dimensions shown.  
Side return air openings must be cut in the field. There are cutting guides stenciled on the cabinet for the side return air  
opening. The size of the opening must not extend beyond the markings on the furnace cabinet.  
2
To minimize pressure drop, the largest opening height possible (up to 14 inches) is preferred.  
FIGURE 9  
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Removing the Bottom Panel  
Horizontal Applications  
Remove the two screws that secure the bottom cap to the  
furnace. Pivot the bottom cap down to release the bottom  
panel. Once the bottom panel has been removed, reinstall  
the bottom cap. See figure 10.  
The SL280UHV furnace can be installed in horizontal ap-  
plications. Order kit number 51W10 (or use equivalent)  
from Lennox.  
Allow for clearances to combustible materials as indicated  
on the unit nameplate. Minimum clearances for closet or al-  
cove installations are shown in figure 11.  
Removing the Bottom Panel  
This furnace may be installed in either an attic or a crawl-  
space. Either suspend the furnace from roof rafters or  
floor joists, as shown in figure12, or install the furnace on a  
platform, as shown in figure 13.  
Typical Horizontal Application  
Unit Suspended in Attic or Crawlspace  
Bracket  
Metal Strap  
Bottom Cap  
3/16 inch  
Air Flow  
Screw  
Bottom Cap  
FIGURE 12  
NOTE − Heavy−gauge perforated sheet metal straps may  
be used to suspend the unit from roof rafters or ceiling  
joists. When straps are used to suspend the unit in this  
way, support must be provided for both the ends. The  
straps must not interfere with the plenum or exhaust pip-  
ing installation. Cooling coils and supply and return air  
plenums must be supported separately.  
Bottom Panel  
FIGURE 10  
Horizontal Application  
Installation Clearances  
Top  
NOTE − When the furnace is installed on a platform in a  
crawlspace, it must be elevated enough to avoid water  
damage and to allow the evaporator coil to drain.  
Left  
End  
Right  
End  
Return Air −− Horizontal Applications  
Bottom  
Type C  
Return air must be brought in through the end of a furnace  
installed in a horizontal application. The furnace is  
equipped with a removable bottom panel to facilitate  
installation. See figure 10.  
Vent Connector  
Type  
Type B1  
Top  
*Front  
Back  
Ends  
Vent  
0
2−1/4 in. (57 mm)**  
0
0
2−14 in. (57 mm)  
0
2 in. (51 mm)  
6 in. (152 mm)  
0‡  
2 in. (51 mm)  
1 in. (25 mm)  
0‡  
Floor  
*Front clearance in alcove installation must be 24 in. (610 mm).  
Maintain a minimum of 24 in. (610 mm) for front service access.  
** 3−1/4 in. if single wall vent pipe is used.  
‡For installations on a combustible floor, do not install the furnace  
directly on carpeting, tile or other combustible materials other  
than wood flooring.  
FIGURE 11  
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TABLE 1  
Horizontal Application  
Unit Installed on Platform  
Filter Size  
Furnace  
Cabinet Width  
Line contact is permissible  
Side Return  
Bottom Return  
See the unit nameplate for  
clearances.  
14−1/2"  
17−1/2"  
21"  
16 X 25 X 1 (1)  
16 X 25 X 1 (1)  
16 X 25 X 1 (1)  
16 X 25 X 1 (2)  
14 X 25 X 1 (1)  
16 X 25 X 1 (1)  
20 X 25 X 1 (1)  
24 X 25 X 1 (1)  
24−1/2"  
GAS  
ENTRY  
VENT  
PIPE  
Duct System  
Use industry-approved standards (such as those pub-  
lished by Air Conditioning Contractors of America or Ameri-  
can Society of Heating, Refrigerating and Air Conditioning  
Engineers) to size and install the supply and return air duct  
system. This will result in a quiet and low-static system that  
has uniform air distribution.  
SERVICE PLATFORM  
NOTE − Do not operate the furnace in the heating mode  
with an external static pressure that exceeds 0.8 inches  
w.c. Higher external static pressures may cause erratic lim-  
it operation.  
FIGURE 13  
Supply Air Plenum  
WARNING  
If the furnace is installed without a cooling coil, a removable  
access panel must be installed in the supply air duct. The  
access panel should be large enough to permit inspection  
(either by smoke or reflected light) of the heat exchanger  
for leaks after the furnace is installed. The furnace access  
panel must always be in place when the furnace is operat-  
ing and it must not allow leaks into the supply air duct sys-  
tem.  
Improper installation of the furnace can result in per-  
sonal injury or death. Combustion and flue products  
must never be allowed to enter the return air system  
or the living space. Use screws and joint tape to seal  
the return air system to the furnace.  
In platform installations with bottom return air, the  
furnace should be sealed airtight to the return air ple-  
num. A door must never be used as a portion of the  
return air duct system. The base must provide a  
stable support and an airtight seal to the furnace. Al-  
low absolutely no sagging, cracks, gaps, etc.  
The return and supply air duct systems must never  
be connected to or from other heating devices such  
as a fireplace or stove, etc. Fire, explosion, carbon  
monoxide poisoning, personal injury and/or proper-  
ty damage could result.  
Return Air Plenum  
NOTE − Return air must not be drawn from a room  
where this furnace, or any other gas−fueled appliance  
(i.e., water heater), or carbon monoxide− producing de-  
vice (i.e., wood fireplace) is installed.  
When return air is drawn from a room, a negative pres-  
sure is created in the room. If agas appliance is operating  
in a room with negative pressure, the flue products can  
be pulled back down the vent pipe and into the room. This  
reverse flow of the flue gas may result in incomplete com-  
bustion and the formation of carbon monoxide gas. This  
toxic gas might then be distributed throughout the house  
by the furnace duct system.  
WARNING  
The inner blower panel must be securely in place  
when the blower and burners are operating. Gas  
fumes, which could contain carbon monoxide, can  
be drawn into living space resulting in personal inju-  
ry or death.  
In upflow applications, the return air can be brought in  
through the bottom or either side of the furnace. If a fur-  
nace with bottom return air is installed on a platform, make  
an airtight seal between the bottom of the furnace and the  
platform to ensure that the unit operates properly and  
safely. Use fiberglass sealing strips, caulking, or equiva-  
lent sealing method between the plenum and the furnace  
cabinet to ensure a tight seal. If a filter is installed, size the  
return air duct to fit the filter frame.  
Filters  
This unit is not equipped with a filter or rack. A field−pro-  
vided high−velocity filter is required for the unit to operate  
properly. Table 1 lists recommended filter sizes.  
A filter must be in place any time the unit is operating.  
Page 12  
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1 − Remove the four mounting screws (figure 14) which  
secure the combustion air inducer / pressure switch  
assembly to the orifice plate. Lift and rotate the assem-  
bly 90 degrees clockwise or counter clockwise to either  
the 3 o’clock position or to 9 o’clock position and re−se-  
cure with four screws. Gasket should be left in place.  
Venting  
A 4−inch diameter flue transition is factory-installed on the  
combustion air inducer outlet of all models. Figure 15  
shows the combustion air inducer as shipped from the  
factory.  
2 − Use tin snips to cut preferred opening on the cabinet  
for repositioning the flue outlet. Use the cut out piece  
as a cover plate to patch unused opening on cabinet.  
Mounting Screws Location  
mounting screws  
UPFLOW POSITION  
Left Side Vent Discharge  
collector box  
cover plate  
pressure  
switch  
vent pipe  
make−up  
box  
mounting screw  
FIGURE 14  
flue  
transition  
UPFlow Position  
UPFLOW POSITION  
Top Vent Discharge  
vent pipe  
FLOW  
AIR  
flue  
transition  
collector box  
S
S
Gas supply piping must be brought into the unit from the right  
side in order to accommodate the flue pipe.  
Remove make−up box assembly (2 screws) and cut wire tie to  
free make−up box wires. Re−install make−up box on other side  
of cabinet.  
pressure  
switch  
S
Re−secure make−up box wires, either pulling excess wires  
through the blower compartment and securing with supplied  
wire tie, or coil excess wire and secure to the gas manifold.  
make−up  
box  
FIGURE 16  
UPFLOW POSITION  
Right Side Vent Discharge  
cover plate  
flue transition  
collector box  
vent pipe  
pressure  
switch  
FLOW  
AIR  
FIGURE 15  
IMPORTANT  
The unit will not vent properly with the flue transition  
pointed down in the 6 o’clock position.  
make−up  
box  
The combustion air inducer may be rotated clock-  
wise or counterclockwise by 90° to allow for top or  
side vent discharge in all applications. When the unit  
is installed, the flue transition must be in the 9  
o’clock, 12 o’clock or 3 o’clock position.  
FLOW  
AIR  
S
Pressure switch tubing may be too long. Cut to  
fit , then re−attach to barbed fitting on pressure  
switch. Tubing must not be allowed to sag.  
If necessary reposition the combustion air inducer, pres-  
sure switch and or make up box as needed per the follow-  
ing steps and see figures 15 through 21.  
FIGURE 17  
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Horizontal Position  
HORIZONTAL RIGHT POSITION  
Top Vent Discharge  
HORIZONTAL LEFT POSITION  
Top Vent Discharge  
vent pipe  
vent pipe  
pressure switch  
pressure switch  
flue transition  
cover plate  
flue  
transition  
AIR  
AIR  
FLOW  
FLOW  
collector box  
cover plate  
make−up box  
collector box  
make−up box  
S
Disconnect pressure switch hose from barbed fitting on the pres-  
sure switch assembly. Remove pressure switch assembly (1  
screw) and cut wire tie to free pressure switch wires. Re−install  
pressure switch on the other side of orifice plate and re−connect  
pressure switch hose.  
S
Gas supply piping must be brought into the unit from the bottom  
in order to accommodate the flue pipe.  
S
Remove make−up box assembly (2 screws) and cut wire tie to  
free make−up box wires. Re−install make−up box on other side  
of cabinet.  
S
Re−secure pressure switch wires by either pulling excess wires  
through the blower compartment and securing with supplied wire  
tie or coil excess wire and secure to the gas manifold.  
S
Re−secure make−up box wires by either pulling excess wires  
through the blower compartment and securing with supplied  
wire tie, or coil excess wire and secure to the gas manifold.  
FIGURE 18  
FIGURE 20  
HORIZONTAL LEFT POSITION  
Side Vent Discharge  
pressure switch  
HORIZONTAL RIGHT POSITION  
Side Vent Discharge  
pressure switch  
AIR  
FLOW  
AIR  
flue transition  
FLOW  
flue transition  
collector box  
collector box  
make−up box  
S
S
Disconnect pressure switch hose from barbed fitting on the  
pressure switch assembly. Remove pressure switch assembly  
(1 screw) and cut wire tie to free pressure switch wires. Re−  
install pressure switch on the other side of orifice plate and re−  
connect pressure switch hose.  
make up box  
FIGURE 21  
Re−secure pressure switch wires by either pulling excess wires  
through the blower compartment and securing with supplied  
wire tie, or coil excess wire and secure to the gas manifold.  
FIGURE 19  
Page 14  
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The SL280UHV series units are classified as fan−assisted  
Category I furnaces when vertically vented according to  
the latest edition of National Fuel Gas Code (NFPA 54 /  
ANSI Z223.1) in the USA. A fan−assisted Category I fur-  
nace is an appliance equipped with an integral mechanical  
means to either draw or force combustion products through  
the combustion chamber and/or heat exchanger. The  
SL280UHV is not approved for use with horizontal venting..  
Use self−drilling sheet metal screws or a mechanical fas-  
tener to firmly secure the vent pipe to the round collar of the  
flue transition. If self−drilling screws are used to attach the  
vent pipe, it is recommended that three be used. Drive one  
self−drilling screw through the front and one through each  
side of the vent pipe and collar. See figures 19, 21 and 22.  
Install the first vent connector elbow at a minimum of six  
inches (152 mm) from the furnace vent outlet. See figure  
22.  
NOTE − Use these instructions as a guide. They do not su-  
persede local codes. This furnace must be vented accord-  
ing to all local codes these installation instructions, and the  
provided venting tables in these instructions  
Venting Using a Masonry Chimney  
The following additional requirements apply when a lined  
masonry chimney is used to vent this furnace.  
Masonry chimneys used to vent Category I central fur-  
naces must be either tile-lined or lined with a listed metal  
lining system or dedicated gas vent. Unlined masonry  
chimneys are prohibited. See figures 23 and 24 for com-  
mon venting.  
The venting tables in this manual were extracted from the  
National Fuel Gas Code (NFPA 54 / ANSI Z223.1) and are  
provided as a guide for proper vent installation. Proper ap-  
plication, termination, construction and location of vents  
must conform to local codes having jurisdiction. In the ab-  
sence of local codes, the NFGC serves as the defining doc-  
ument.  
A chimney with one or more sides exposed to the outside of  
the structure is considered to be an exterior chimney.  
An exterior masonry chimney that is not tile−lined must be  
lined with B1 vent or a listed insulated flexible metal vent.  
An exterior tile−lined chimney that is sealed and capped  
may be lined with a listed uninsulated flexible metal vent.  
Refer to the tables and the venting information contained in  
these instructions to properly size and install the venting  
system.  
If the existing chimney will not accommodate a listed metal  
liner, either the chimney must be rebuilt to accommodate  
one of these liners or an alternate approved venting meth-  
od must be found.  
IMPORTANT  
Once the venting system is installed, attach the ꢀDis-  
connected Vent" warning sticker to a visible area of  
the plenum near the vent pipe. See figure 22. The  
warning sticker is provided in the bag assembly. Or-  
der kit 66W04 for additional stickers.  
Insulation for the flexible vent pipe must be an encapsu-  
lated fiberglass sleeve recommended by the flexible vent  
pipe manufacturer. See figure 23.  
Common Venting Using Metal−Lined Masonry Chimney  
SEALED  
WARNING  
Asphyxiation hazard. The exhaust vent for this fur-  
nace must be securely connected to the furnace flue  
transition at all times.  
MAX. LENGTH  
−− SEE NOTE 1  
BELOW.  
5 ft. (1.5 m)  
minimum  
MIN. LENGTH −− AS  
SHORT AS PRACTICAL  
EXTERIOR  
CHIMNEY WITH  
METAL  
LINER  
VENT CONNECTION  
“DISCONNECTED VENT”  
VENT CONNECTOR  
WARNING  
STICKER  
VENT PIPE  
(min. 6" length)  
4 in. (102 mm)  
minimum  
FURNACE  
OTHER  
APPLIANCE  
PERMANENTLY  
SEALED FIREPLACE  
OPENING  
AIR FLOW  
FLUE TRANSITION  
COLLAR  
NOTE 1 − Refer to the provided venting tables for installations. Refer  
to the capacity requirements shown in the provided venting tables.  
FIGURE 23  
FIGURE 22  
Page 15  
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Common Venting Using Tile−Lined Interior Masonry Chimney and Combined Vent Connector  
MINIMUM LENGTH = AS SHORT AS PRACTICAL.  
FOR MAXIMUM LENGTH SEE NOTE TO LEFT  
INTERIOR TILE−LINED  
MASONRY CHIMNEY  
NOTE− Refer to provided venting tables  
for installations.  
NOTE − the chimney must be properly  
sized per provided venting tables or  
lined with listed metal lining system.  
VENT  
CONNECTOR  
OTHER  
APPLIANCE  
PERMANENTLY  
SEALED FIREPLACE  
OPENING  
FURNACE  
AIR FLOW  
FIGURE 24  
Never connect a Category I appliance to a chimney that is  
servicing a solid−fuel appliance. If a fireplace chimney flue  
is used to vent this appliance, the fireplace opening must  
be permanently sealed.  
DO NOT insulate the space between the liner and the  
chimney wall with puffed mica or any other loose gran-  
ular insulating material  
A type B or listed chimney lining system that passes  
through an unused masonry chimney flue is not considered  
to be exposed to the outdoors.  
IMPORTANT  
SINGLE appliance venting of a fan-assisted furnace  
into a tile-lined masonry chimney (interior or outside  
wall) is PROHIBITED. The chimney must first be lined  
with either type B1 vent or an insulated single wall  
flexible vent lining system which has been sized ac-  
cording to the provided venting tables and the vent  
pipe manufacturer’s instructions.  
General Venting Requirements  
Vent all SL280UHV furnaces according to these instruc-  
tions:  
1 − Vent diameter recommendations and maximum allow-  
able piping runs are found in the provided venting  
tables.  
A fan−assisted furnace may be commonly vented into an  
existing lined masonry chimney if the following conditions  
are met:  
2 − In no case should the vent or vent connector diameter  
be less than the diameter specified in the provided  
venting tables.  
S The chimney is currently serving at least one drafthood  
equipped appliance  
3 − The minimum vent capacity determined by the sizing  
tables must be less than the low fire input rating and the  
maximum vent capacity must be greater than the high  
fire input rating.  
S The vent connectors and chimney are sized according  
to the provided venting tables.  
If type B1 double-wall vent is used inside a chimney, no oth-  
er appliance can be vented into the chimney. The outer wall  
of type B1 vent pipe must not be exposed to flue products.  
4 − Single appliance vents − If the vertical vent or tile-lined  
chimney has a larger diameter or flow area than the  
vent connector, use the vertical vent diameter to de-  
termine the minimum vent capacity and the vent  
connector diameter to determine the maximum vent  
capacity. The flow area of the vertical vent, however,  
shall not exceed 7 times the flow area of the listed ap-  
pliance categorized vent area, drafthood outlet area or  
flue collar area unless designed according to approved  
engineering methods.  
A type B1 vent or masonry chimney liner shall terminate  
above the roof surface with a listed cap or a listed roof as-  
sembly according to the terms of their respective listings  
and the vent manufacturer’s instructions.  
When inspection reveals that an existing chimney is not  
safe for the intended purpose, it shall be rebuilt to conform  
to nationally recognized standards, lined or relined with  
suitable materials, or replaced with a gas vent or chimney  
suitable for venting SL280UHV series units. The chimney  
passageway must be checked periodically to ensure that it  
is clear and free of obstructions.  
5 − Multiple appliance vents − The flow area of the largest  
section of vertical vent or chimney shall not exceed 7  
times the smallest listed appliance categorized vent  
area, drafthood outlet area or flue collar area unless de-  
signed according to approved engineering methods.  
Do not install a manual damper, barometric draft regulator,  
or flue restrictor between the furnace and the chimney.  
Page 16  
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6 − The entire length of single wall metal vent connector  
shall be readily accessible for inspection, cleaning,  
and replacement.  
flue collar by self−drilling screws or other approved  
means, except vent connectors of listed type B vent  
material which shall be assembled according to the  
manufacturer’s instructions. Joints between sections  
of single wall connector piping shall be fastened by  
screws or other approved means.  
7 − Single appliance venting configurations with zero lat-  
eral lengths (tables 3 and 4) are assumed to have no  
elbows in the vent system. For all other vent configura-  
tions, the vent system is assumed to have two 90° el-  
bows. For each additional 90° elbow or equivalent (for  
example two 45° elbows equal one 90° elbow) beyond  
two, the maximum capacity listed in the venting table  
should be reduced by 10% (0.90 x maximum listed ca-  
pacity).  
13 − When the vent connector used for Category I ap-  
pliances must be located in or pass through a crawl-  
space, attic or other areas which may be cold, that por-  
tion of the vent connector shall be constructed of listed  
double-wall type B vent material or material having  
equivalent insulation qualities.  
14 − All venting pipe passing through floors, walls, and ceil-  
ings must be installed with the listed clearance to com-  
bustible materials and be fire stopped according to lo-  
cal codes. In absence of local codes, refer to NFGC  
(Z223.1).  
8 − The common venting tables (5, 6, 7, and 8) were gen-  
erated using a maximum horizontal vent connector  
length of 1−1/2 feet (.46 m) for each inch (25 mm) of  
connector diameter as follows:  
TABLE 2  
15 − No portion of the venting system can extend into, or pass  
through any circulation air duct or plenum.  
Maximum Horizontal  
Connector Length feet (m)  
Connector Diameter  
inches (mm)  
16 − Vent connectors serving Category I appliances shall  
not be connected to any portion of mechanical draft  
systems operating under positive pressure such as  
Category III or IV venting systems.  
3 (76)  
4 (102)  
5 (127)  
6 (152)  
7 (178)  
4−1/2 (1.37)  
6 (1.83)  
7−1/2 (2.29)  
9 (2.74)  
17 − If vent connectors are combined prior to entering the  
common vent, the maximum common vent capacity  
listed in the common venting tables must be reduced by  
10%, the equivalent of one 90° elbow (0.90 x maximum  
common vent capacity).  
10−1/2 (3.20)  
9 − If the common vertical vent is offset, the maximum  
common vent capacity listed in the common venting  
tables should be reduced by 20%, the equivalent of two  
90° elbows (0.80 x maximum common vent capacity).  
The horizontal length of the offset shall not exceed  
1-1/2 feet (.46 m) for each inch (25 mm) of common  
vent diameter.  
18 − The common vent diameter must always be at least as  
large as the largest vent connector diameter.  
19 − In no case, shall the vent connector be sized more than  
two consecutive table size diameters over the size of  
the draft hood outlet or flue collar outlet.  
20 − Do not install a manual damper, barometric draft regu-  
lator or flue restrictor between the furnace and the  
chimney.  
10 − The vent pipe should be as short as possible with the  
least number of elbows and angles required to com-  
plete the job. Route the vent connector to the vent us-  
ing the shortest possible route.  
21 − When connecting this appliance to an existing dedi-  
cated or common venting system, you must inspect the  
venting system’s general condition and look for signs  
of corrosion. The existing vent pipe size must conform  
to these instructions and the provided venting tables. If  
the existing venting system does not meet these re-  
quirements, it must be resized.  
11 − A vent connector shall be supported without any dips  
or sags and shall slope a minimum of 1/4 inch (6.4 mm)  
per linear foot (305 mm) of connector, back toward the  
appliance.  
12 − Vent connectors shall be firmly attached to the furnace  
Page 17  
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TABLE 3  
Capacity of Type B Double−Wall Vents with Type B Double−Wall Connectors  
Serving a Single Category I Appliance  
Vent and Connector Diameter − D (inches)  
Height  
H
(feet)  
Lateral  
L
(feet)  
3 Inch  
4 Inch  
5 Inch  
6 Inch  
Appliance Input Rating in Thousands of Btu Per Hour  
MIN  
0
MAX  
78  
51  
49  
46  
84  
57  
53  
49  
88  
61  
57  
51  
94  
69  
65  
59  
53  
97  
75  
71  
64  
58  
52  
100  
81  
77  
70  
64  
58  
NR  
MIN  
0
MAX  
152  
97  
MIN  
0
MAX  
251  
157  
153  
149  
276  
178  
171  
164  
295  
194  
187  
176  
327  
226  
219  
206  
195  
349  
250  
242  
229  
217  
206  
374  
283  
275  
262  
249  
237  
214  
MIN  
0
MAX  
375  
232  
227  
223  
415  
263  
255  
247  
447  
289  
280  
267  
502  
339  
330  
315  
301  
540  
377  
367  
351  
337  
322  
587  
432  
421  
405  
389  
374  
346  
0
2
13  
21  
25  
0
18  
30  
36  
0
27  
39  
47  
0
32  
50  
59  
0
6
8
4
94  
6
91  
0
165  
109  
103  
98  
2
12  
23  
28  
0
16  
32  
39  
0
25  
42  
51  
0
28  
53  
64  
0
5
8
0
175  
118  
113  
104  
191  
136  
130  
121  
112  
202  
149  
143  
133  
124  
116  
213  
166  
160  
150  
141  
132  
113  
2
12  
23  
30  
0
17  
32  
41  
0
23  
41  
54  
0
26  
52  
67  
0
10  
5
10  
0
2
11  
22  
29  
35  
0
15  
30  
40  
48  
0
20  
39  
51  
61  
0
22  
49  
64  
76  
0
5
15  
10  
15  
0
2
10  
21  
28  
34  
48  
0
14  
29  
38  
46  
55  
0
18  
38  
50  
59  
69  
0
20  
47  
62  
73  
84  
0
5
20  
10  
15  
20  
0
2
9
13  
28  
37  
44  
53  
73  
14  
36  
48  
57  
66  
88  
18  
45  
59  
70  
80  
104  
5
21  
27  
33  
56  
NR  
10  
15  
20  
30  
30  
NOTE − Single appliance venting configurations with zero lateral lengths are assumed to have no elbows in the vent system. For all other  
vent configurations, the vent system is assumed to have two 90° elbows. For each additional 90° elbow or equivalent (for example two 45°  
elbows equal one 90° elbow) beyond two, the maximum capacity listed in the venting table should be reduced by 10 percent (0.90 x maxi-  
mum listed capacity).  
Page 18  
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TABLE 4  
Capacity of Type B Double−Wall Vents with Single−Wall Metal Connectors  
Serving a Single Category I Appliance  
Vent and Connector Diameter − D (inches)  
Height  
H
(feet)  
Lateral  
L
(feet)  
3 Inch  
4 Inch  
5 Inch  
6 Inch  
Appliance Input Rating in Thousands of Btu Per Hour  
MIN  
38  
MAX  
77  
MIN  
59  
60  
74  
83  
58  
59  
77  
90  
57  
59  
76  
97  
56  
57  
75  
95  
NR  
54  
56  
73  
93  
NR  
NR  
53  
55  
72  
91  
115  
NR  
NR  
MAX  
151  
96  
MIN  
85  
MAX  
249  
156  
152  
147  
273  
176  
168  
161  
293  
193  
185  
171  
325  
225  
216  
201  
186  
346  
248  
239  
223  
208  
192  
372  
281  
271  
255  
239  
223  
NR  
MIN  
126  
123  
146  
163  
123  
121  
151  
175  
120  
119  
148  
188  
116  
115  
144  
182  
220  
114  
113  
141  
177  
216  
254  
110  
109  
136  
171  
208  
246  
NR  
MAX  
373  
231  
225  
220  
412  
261  
252  
243  
444  
287  
277  
261  
499  
337  
326  
308  
290  
537  
375  
363  
344  
325  
306  
584  
429  
417  
397  
377  
357  
NR  
0
2
39  
51  
85  
6
8
4
NR  
NR  
37  
NR  
NR  
83  
92  
102  
114  
83  
6
89  
0
164  
108  
102  
95  
2
39  
56  
83  
5
NR  
NR  
37  
NR  
NR  
87  
107  
122  
82  
8
0
174  
117  
111  
100  
190  
136  
128  
116  
NR  
200  
148  
140  
129  
NR  
NR  
211  
164  
157  
144  
131  
NR  
NR  
2
39  
61  
82  
10  
5
52  
56  
105  
132  
80  
10  
0
NR  
36  
NR  
93  
2
38  
69  
80  
5
51  
63  
102  
128  
158  
78  
15  
10  
15  
0
NR  
NR  
35  
NR  
NR  
96  
2
37  
74  
78  
5
50  
68  
100  
125  
155  
186  
76  
20  
10  
15  
20  
0
NR  
NR  
NR  
34  
NR  
NR  
NR  
99  
2
37  
80  
76  
5
49  
74  
98  
10  
15  
20  
30  
NR  
NR  
NR  
NR  
NR  
NR  
NR  
NR  
122  
151  
181  
NR  
30  
NOTE − Single appliance venting configurations with zero lateral lengths are assumed to have no elbows in the vent system. For all other  
vent configurations, the vent system is assumed to have two 90° elbows. For each additional 90° elbow or equivalent (for example two 45°  
elbows equal one 90° elbow) beyond two, the maximum capacity listed in the venting table should be reduced by 10 percent (0.90 x maxi-  
mum listed capacity).  
Page 19  
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TABLE 5  
Vent Connector Capacity  
Type B Double−Wall Vents with Type B Double−Wall Connectors  
Serving Two or More Category I Appliances  
Vent and Connector Diameter − D (inches)  
Vent  
Height  
H
Connector  
Rise  
3 Inch  
4 Inch  
5 Inch  
6 Inch  
R
(feet)  
Appliance Input Rating in Thousands of Btu Per Hour  
(feet)  
MIN  
22  
23  
24  
22  
23  
24  
22  
23  
24  
21  
22  
24  
21  
22  
23  
20  
21  
22  
MAX  
37  
41  
44  
40  
44  
47  
43  
47  
50  
50  
53  
55  
54  
57  
60  
62  
64  
66  
MIN  
35  
37  
38  
35  
36  
37  
34  
36  
37  
33  
35  
36  
33  
34  
35  
31  
33  
34  
MAX  
66  
MIN  
46  
48  
49  
49  
51  
53  
49  
51  
52  
47  
49  
51  
46  
48  
50  
45  
47  
48  
MAX  
106  
121  
132  
114  
128  
139  
123  
136  
146  
142  
153  
163  
157  
167  
176  
181  
190  
198  
MIN  
58  
60  
62  
64  
66  
67  
65  
67  
69  
64  
66  
68  
62  
64  
66  
60  
62  
64  
MAX  
164  
183  
199  
176  
195  
210  
189  
206  
220  
220  
235  
248  
246  
259  
271  
288  
299  
309  
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
75  
6
81  
72  
80  
8
87  
78  
86  
10  
15  
20  
30  
92  
89  
96  
102  
99  
105  
110  
113  
118  
123  
TABLE 6  
Common Vent Capacity  
Type B Double−Wall Vents with Type B Double−Wall Connectors  
Serving Two or More Category I Appliances  
Common Vent Diameter − D (inches)  
Vent  
Height  
H
4 Inch  
5 Inch  
6 Inch  
7 Inch  
Appliance Input Rating in Thousands of Btu Per Hour  
(feet)  
FAN + FAN  
92  
FAN + NAT  
FAN + FAN  
140  
FAN + NAT  
116  
FAN + FAN  
204  
FAN + NAT  
161  
FAN + FAN  
309  
FAN + NAT  
248  
6
81  
90  
8
101  
155  
129  
224  
178  
339  
275  
10  
15  
20  
30  
110  
97  
169  
141  
243  
194  
367  
299  
125  
112  
123  
138  
195  
164  
283  
228  
427  
352  
136  
215  
183  
314  
255  
475  
394  
152  
244  
210  
361  
297  
547  
459  
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TABLE 7  
Vent Connector Capacity  
Type B Double−Wall Vents with Single−Wall Metal Connectors  
Serving Two or More Category I Appliances  
Vent and Connector Diameter − D (inches)  
Height  
H
(feet)  
Lateral  
L
(feet)  
3 Inch  
4 Inch  
5 Inch  
6 Inch  
Appliance Input Rating in Thousands of Btu Per Hour  
MIN  
NR  
NR  
NR  
NR  
NR  
NR  
NR  
NR  
NR  
NR  
NR  
NR  
49  
MAX  
NR  
NR  
NR  
NR  
NR  
NR  
NR  
NR  
NR  
NR  
NR  
NR  
56  
MIN  
NR  
NR  
NR  
NR  
NR  
NR  
NR  
84  
MAX  
NR  
NR  
NR  
NR  
NR  
NR  
NR  
85  
MIN  
NR  
MAX  
NR  
MIN  
NR  
MAX  
NR  
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
NR  
NR  
168  
175  
NR  
182  
198  
NR  
6
121  
NR  
131  
NA  
125  
130  
119  
124  
129  
116  
121  
127  
115  
120  
125  
112  
117  
122  
126  
138  
121  
134  
144  
138  
150  
160  
152  
163  
172  
175  
185  
193  
184  
191  
182  
189  
197  
177  
185  
193  
175  
182  
190  
169  
177  
185  
193  
208  
186  
203  
217  
214  
230  
243  
238  
252  
264  
278  
290  
300  
8
10  
15  
20  
30  
89  
91  
79  
87  
83  
94  
87  
100  
97  
78  
52  
59  
82  
103  
107  
110  
115  
119  
55  
62  
87  
47  
60  
77  
51  
62  
81  
54  
64  
85  
NOTE − Single appliance venting configurations with zero lateral lengths are assumed to have no elbows in the vent system. For all other  
vent configurations, the vent system is assumed to have two 90° elbows. For each additional 90° elbow or equivalent (for example two 45°  
elbows equal one 90° elbow) beyond two, the maximum capacity listed in the venting table should be reduced by 10 percent (0.90 x maxi-  
mum listed capacity).  
TABLE 8  
Common Vent Capacity  
Type B Double−Wall Vents with Single−Wall Metal Connectors  
Serving Two or More Category I Appliances  
Common Vent Diameter − D (inches)  
Vent  
4 Inch  
5 Inch  
6 Inch  
7 Inch  
Height  
H
(feet)  
Appliance Input Rating in Thousands of Btu Per Hour  
FAN + FAN  
FAN + NAT  
FAN + FAN  
NA  
FAN + NAT  
113  
FAN + FAN  
200  
FAN + NAT  
158  
FAN + FAN  
FAN + NAT  
244  
6
NA  
NA  
78  
87  
304  
331  
357  
416  
463  
533  
8
NA  
126  
218  
173  
269  
10  
15  
20  
30  
NA  
94  
163  
137  
237  
189  
292  
121  
131  
145  
108  
118  
132  
189  
159  
275  
221  
343  
208  
177  
305  
247  
383  
236  
202  
350  
286  
446  
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Removal of the Furnace from Common Vent  
3 − Close all building doors and windows and all doors be-  
tween the space in which the appliances remaining  
connected to the common venting system are located  
and other spaces of the building. Turn on clothes dry-  
ers and any appliances not connected to the common  
venting system. Turn on any exhaust fans, such as  
range hoods and bathroom exhausts, so they will oper-  
ate at maximum speed. Do not operate a summer ex-  
haust fan. Close fireplace dampers.  
In the event that an existing furnace is removed from a  
venting system commonly run with separate gas ap-  
pliances, the venting system is likely to be too large to  
properly vent the remaining attached appliances.  
Conduct the following test while each appliance is operat-  
ing and the other appliances (which are not operating) re-  
main connected to the common venting system. If the  
venting system has been installed improperly, you must  
correct the system as indicated in the general venting re-  
quirements section.  
4 − Follow the lighting instructions. Turn on the appliance  
that is being inspected. Adjust the thermostat so that  
the appliance operates continuously.  
WARNING  
CARBON MONOXIDE POISONING HAZARD  
5 − After the main burner has operated for 5 minutes, test  
for leaks of flue gases at the draft hood relief opening.  
Use the flame of a match or candle, or smoke from a  
cigarette, cigar, or pipe.  
Failure to follow the steps outlined below for each  
appliance connected to the venting system being  
placed into operation could result in carbon mon-  
oxide poisoning or death.  
The following steps shall be followed for each ap-  
pliance connected to the venting system being  
placed into operation, while all other appliances  
connected to the venting system are not in  
operation:  
6 − After determining that each appliance connected to the  
common venting system is venting properly, (step 3)  
return all doors, widows, exhaust fans, fireplace damp-  
ers, and any other gas−burning appliances to their pre-  
vious mode of operation.  
7 − If a venting problem is found during any of the preced-  
ing tests, the common venting system must be modi-  
fied to correct the problem.  
1 − Seal any unused openings in the common venting sys-  
tem.  
2 − Inspect the venting system for proper size and horizontal  
pitch. Determine that there is no blockage, restriction,  
leakage, corrosion, or other deficiencies which could  
cause an unsafe condition.  
Resize the common venting system to the minimum  
vent pipe size determined by using the appropriate  
tables in Appendix G. (These are in the current stan-  
dards of the National Fuel Gas Code ANSI Z223.1.  
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4 − The piping should be sloped 1/4 inch (6.4 mm) per 15  
feet (4.57 m) upward toward the meter from the fur-  
nace. The piping must be supported at proper intervals  
[every 8 to 10 feet (2.44 to 3.01 m)] with suitable hang-  
ers or straps. Install a drip leg in vertical pipe runs to the  
unit.  
Gas Piping  
CAUTION  
If a flexible gas connector is required or allowed by  
the authority that has jurisdiction, black iron pipe  
shall be installed at the gas valve and extend outside  
the furnace cabinet. The flexible connector can then  
be added between the black iron pipe and the gas  
supply line.  
5 − A 1/8" N.P.T. plugged tap or pressure post is located  
on the gas valve to facilitate test gauge connection.  
See figures 35 and 36.  
6 − In some localities, codes may require the installation of  
a manual main shut-off valve and union (furnished by  
the installer) external to the unit. The union must be of  
the ground joint type.  
Gas Supply  
1 − This unit is shipped standard for left or right side instal-  
lation of gas piping (or top entry in horizontal applica-  
tions). Connect the gas supply to the piping assembly.  
IMPORTANT  
Compounds used on threaded joints of gas piping  
must be resistant to the actions of liquified petro-  
leum gases.  
2 − When connecting the gas supply piping, consider fac-  
tors such as length of run, number of fittings, and fur-  
nace rating to avoid excessive pressure drop. Table 9  
lists recommended pipe sizes for typical applications.  
NOTE − If emergency shutoff is necessary, shut off the main  
manual gas valve and disconnect main power to the fur-  
nace. The installer should properly label these devices.  
3 − The gas piping must not run in or through air ducts,  
clothes chutes, gas vents or chimneys, dumb waiters,  
or elevator shafts.  
TABLE 9  
3
3
Gas Pipe Capacity − ft /hr (m /hr)  
Nominal  
Iron Pipe  
Size  
inches  
(mm)  
Length of Pipe − feet (m)  
Internal  
Diameter  
inches  
(mm)  
10  
(3.048)  
20  
(6.096)  
30  
(9.144)  
40  
50  
60  
70  
80  
90  
100  
(12.192) (15.240) (18.288) (21.336) (24.384) (27.432) (30.480)  
1/2  
(12.7)  
.622  
(17.799)  
175  
(4.96)  
120  
(3.40)  
97  
(2.75)  
82  
(2.32)  
73  
(2.07)  
66  
(1.87)  
61  
(1.73)  
57  
(1.61)  
53  
(1.50)  
50  
(1.42)  
3/4  
(19.05)  
.824  
(20.930)  
360  
(10.19)  
250  
(7.08)  
200  
(5.66)  
170  
(4.81)  
151  
(4.28)  
138  
(3.91)  
125  
(3.54)  
118  
(3.34)  
110  
(3.11)  
103  
(2.92)  
1
(25.4)  
1.049  
(26.645)  
680 465  
(919.25) (13.17)  
375  
(10.62)  
320  
(9.06)  
285  
(8.07)  
260  
(7.36)  
240  
(6.80)  
220  
(6.23)  
205  
(5.80)  
195  
(5.52)  
1−1/4  
(31.75)  
1.380  
(35.052)  
1400  
(39.64)  
950  
(26.90)  
770  
(21.80)  
660  
(18.69)  
580  
(16.42)  
530  
(15.01)  
490  
(13.87)  
460  
(13.03)  
430  
(12.18)  
400  
(11.33)  
1−1/2  
(38.1)  
1.610  
(40.894)  
2100  
(59.46)  
460  
(41.34)  
1180  
(33.41)  
990  
(28.03)  
900  
(25.48)  
810  
(22.94)  
750  
(21.24)  
690  
(19.54)  
650  
(18.41)  
620  
(17.56)  
2
(50.8)  
2.067  
(52.502)  
3950  
(111.85)  
2750  
(77.87)  
2200  
(62.30)  
1900  
(53.80)  
1680  
(47.57)  
1520  
(43.04)  
1400  
(39.64)  
1300  
(36.81)  
1220  
(34.55)  
1150  
(32.56)  
2−1/2  
(63.5)  
2.469  
(67.713)  
6300 4350  
(178.39) (123.17)  
3520  
(99.67)  
3000  
(84.95  
2650  
(75.04)  
2400  
(67.96)  
2250  
(63.71)  
2050  
(58.05)  
1950  
(55.22)  
1850  
(52.38)  
3
(76.2)  
3.068  
(77.927)  
11000 7700  
6250  
5300  
4750  
4300  
3900  
3700  
(311.48) (218.03) (176.98) (150.07) (134.50) (121.76) (110.43) (104.77)  
3450  
(97.69)  
3250  
(92.03)  
3
NOTE − Capacity given in cubic feet (m ) of gas per hour and based on 0.60 specific gravity gas.  
Page 23  
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Left Side Piping  
(Standard)  
MANUAL  
MAIN SHUT−OFF  
VALVE  
(With 1/8 in. NPT  
Plugged Tap  
Shown)  
AUTOMATIC  
GAS VALVE  
MANUAL  
MAIN SHUT−OFF  
VALVE  
AUTOMATIC  
GAS VALVE  
(With 1/8 in. NPT  
Plugged Tap Shown)  
GROUND  
JOINT  
UNION  
GROUND  
JOINT  
UNION  
DRIP LEG  
Right Side Piping  
(Alternate)  
FIELD  
PROVIDED  
AND INSTALLED  
DRIP LEG  
NOTE − BLACK IRON PIPE ONLY TO BE ROUTED INSIDE OF CABINET  
FIGURE 25  
Horizontal Applications  
Possible Gas Piping Configurations  
MANUAL  
MAIN SHUT−OFF  
VALVE  
MANUAL  
MAIN SHUT−OFF  
VALVE  
Horizontal Application  
Left−Side Air Discharge  
GROUND  
JOINT  
UNION  
GROUND  
JOINT  
UNION  
DRIP LEG  
DRIP LEG  
MANUAL  
MAIN SHUT−OFF  
VALVE  
FIELD  
PROVIDED  
AND  
GROUND  
JOINT  
UNION  
INSTALLED  
Horizontal Application  
Right−Side Air Discharge  
NOTE − BLACK IRON PIPE ONLY TO BE ROUTED INSIDE OF CABINET  
DRIP LEG  
FIGURE 26  
Leak Check  
supply system the during any pressure testing of the gas  
supply system at pressures less than or equal to 1/2 psig  
(3.48 kPa, 14 inches w.c.).  
After gas piping is completed, carefully check all piping  
connections (factory− and field−installed) for gas leaks. Use  
a leak detecting solution or other preferred means.  
NOTE − If emergency shutoff is necessary, shut off the main  
manual gas valve and disconnect the main power to the  
furnace. The installer should properly label these devices.  
IMPORTANT  
When testing pressure of gas lines, gas valve must  
be disconnected and isolated. See figure 27. Gas  
valves can be damaged if subjected to pressures  
greater than 1/2 psig (3.48 kPa, 14 inches w.c.).  
CAUTION  
Some soaps used for leak detection are corrosive to  
certain metals. Carefully rinse piping thoroughly af-  
ter leak test has been completed. Do not use  
matches, candles, flame or other sources of ignition  
to check for gas leaks.  
MANUAL MAIN  
ISOLATE  
SHUT−OFF VALVE  
WILL NOT HOLD  
GAS VALVE  
FURNACE  
NORMAL TEST  
PRESSURE  
1/8 NPT PLUG  
CAP  
The furnace must be isolated by closing its individual  
manual shut-off valve and disconnecting from from the gas  
FIGURE 27  
Page 24  
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Refer to figure 33 for unit field wiring. See figures 30 and 31  
®
Electrical  
for icomfort Touch thermostat wiring in communicating  
ELECTROSTATIC DISCHARGE (ESD)  
applications. Table 11 shows DIP switch and on−board link  
settings for non−communicating thermostat applications.  
Typical wiring schematic is shown in figure 32.  
Precautions and Procedures  
CAUTION  
1 − The power supply wiring must meet Class I restric-  
tions. Protected by either a fuse or circuit breaker, se-  
lect circuit protection and wire size according to unit  
nameplate.  
Electrostatic discharge can affect elec-  
tronic components. Take precautions to  
neutralize electrostatic charge by  
touching your hand and tools to metal  
prior to handling the control.  
NOTE − Unit nameplate states maximum current draw.  
Maximum over−current protection allowed is shown in table  
10.  
The unit is equipped with a field make−up box on the left  
hand side of the cabinet. The make−up box may be moved  
to the right side of the furnace to facilitate installation. If the  
make−up box is moved to the right side, clip the wire ties  
that bundle the wires together. The excess wire must be  
pulled into the blower compartment. Secure the excess  
wire to the existing harness to protect it from damage.  
TABLE 10  
Maximum Over−Current  
SL280UH Model  
Protection (Amps)  
070V36A, 09036B  
15  
20  
090V48B, 090V60C, 110V60C,  
135V60D  
INTERIOR MAKE−UP BOX INSTALLATION  
Left side  
2 − Holes are on both sides of the furnace cabinet to facili-  
tate wiring.  
3 − Install a separate (properly sized) disconnect switch  
near the furnace so that power can be turned off for  
servicing.  
BOX  
4 − Before connecting the thermostat or the power wiring,  
check to make sure the wires will be long enough for  
servicing at a later date. Remove the blower access  
panel to check the length of the wire.  
5 − Complete the wiring connections to the equipment.  
Use the provided unit wiring diagram and the field wir-  
ing diagrams shown in table 11 and figure 33. Use  
18−gauge wire or larger that is suitable for Class II ra-  
ting for thermostat connections.  
FIGURE 28  
INTERIOR MAKE−UP BOX INSTALLATION  
6 − Electrically ground the unit according to local codes or,  
in the absence of local codes, according to the current  
National Electric Code (ANSI/NFPA No. 70). A green  
ground wire is provided in the field make−up box.  
NOTE −The SL280UHV furnace contains electronic  
components that are polarity sensitive. Make sure  
that the furnace is wired correctly and is properly  
grounded.  
Right Side  
BOX  
7 − One line voltage ꢁACC" 1/4" spade terminal is provided  
on the furnace integrated control. Any electronic air  
cleaner or other accessory rated up to one amp can be  
connected to this terminal with the neutral leg of the cir-  
cuit being connected to the one of the provided neutral  
terminals. See figure 34 for control configuration. This  
terminal is energized when the indoor blower is operat-  
ing.  
FIGURE 29  
Page 25  
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8 − An unpowered, normally open (dry) set of contacts with  
a 1/4" spade terminal ꢁHUM" are provided for humidifi-  
er connections and may be connected to 24V or 120V.  
Any humidifier rated up to one amp can be connected  
to these terminals. In 120V humidifier applications the  
neutral leg of the circuit can be connected to one of the  
provided neutral terminals. This terminal is energized  
in the heating mode.  
Indoor Blower Speeds  
Non−Communicating  
1 − When the thermostat is set to ꢁFAN ON," the indoor  
blower will run continuously at a field selectable per-  
centage of the second−stage cooling speed when there  
is no cooling or heating demand. The factory default  
setting is 38% of cool speed.  
9 − Install the room thermostat according to the instruc-  
tions provided with the thermostat. See table 11 for  
field wiring connections in varying applications. If the  
furnace is being matched with a heat pump, refer to the  
instruction packaged with the dual fuel thermostat.  
2 − When the SL280UHV is running in the heating mode,  
the indoor blower will run on the heating speed desig-  
nated by the positions of DIP switches 11, 12 and 13.  
First stage heating will run at 91% heat speed.  
3 − When there is a cooling demand, the indoor blower will  
run on the cooling speed designated by the positions  
of DIP switches 5 and 6. First stage cooling will run at  
70% cool speed.  
Thermostat Selection  
CAUTION  
Field wiring for both communicating and non−com-  
municating applications is illustrated in diagrams,  
which begin on Page 27.  
Communicating  
NOTE − When the SL280UHV is used with icomfort  
®
Touch thermostat, proper indoor blower speed selec-  
tions are made by the communicating thermostat.  
Non−Communicating  
In non−communicating applications the SL280UHV is de-  
signed to operate in a SINGLE−STAGE mode or TWO−  
STAGE mode using a conventional thermostat.  
1 − When the thermostat is set to ꢁFAN ON," the indoor  
blower will run at setting determined during system  
configuration.  
For optimal performance in non−communicating applica-  
®
2 − When there is a heating demand the fan will run on  
heating speeds for firing rate.  
tions, Lennox recommends use of a ComfortSense 7000  
high quality electronic digital thermostat or any other with  
adjustable settings for 1st stage / 2nd stage on / off differen-  
tials and adjustable stage timers.  
3 − When there is a cooling demand, the fan will run on the  
first stage and second stage cooling speed set using  
the icomfort Touch® thermostat in the installer setup  
mode. The factory default is based upon 400 CFM a  
ton.  
Lennox recommends the following two−stage thermostat  
settings:  
First heat stage differential set to 1/2 to 1 degree F; second  
heat stage differential set to 1/2 or 1 degree F; second heat  
stage upstage timer disabled, or set to maximum (1 hr mini-  
mum).  
Generator Use − Voltage Requirements  
The following requirements must be kept in mind when  
specifying a generator for use with this equipment:  
Communicating  
S
S
S
The furnace requires 120 volts (Range: 102 volts to  
132 volts)  
®
In communicating applications the icomfort Touch ther-  
mostat must be used. Refer to the instructions provided  
with the thermostat for installation, set−up and operation. In  
communicating system all unused thermostat wire in the  
wire bundle needs to be terminated inside and out. The ex-  
The furnace operates at 60 Hz + 5% (Range: 57 Hz to  
63 Hz)  
The furnace integrated control requires both correct  
polarity and proper ground. Both polarity and proper  
grounding should be checked before attempting to op-  
erate the furnace on either permanent or temporary  
power  
tra wires can terminate on the ’C" terminal of the icomfort  
t
communication terminal strip. (RSBus). Using an addition-  
al wire come off "C" terminal and wire nut all the extra wires  
together. Termination on the outdoor control must match  
the indoor control.  
S
Generator should have a wave form distortion of less  
than 5% THD (total harmonic distortion)  
Page 26  
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®
®
icomfort Touch Thermostat with SL280UHV  
and Non−Communicating Outdoor Unit  
icomfort Touch Thermostat with SL280UHV  
and icomfortt−ENABLED Outdoor Unit  
®
®
icomfort Touch Thermostat  
icomfortt−Enabled SL280UHV Indoor Furnace  
Non−Communicating Outdoor Air Conditioner  
icomfort Touch Thermostat  
icomfortt−Enabled SL280UHV Indoor Furnace  
icomfortt−Enabled Outdoor Air Conditioner or Heat Pump  
icomfortt−  
ENABLED  
SL280UHV  
icomfortt−  
ENABLED  
SL280UHV  
FURNACE  
FURNACE  
OPTIONAL  
DISCHARGE  
AIR SENSOR  
OPTIONAL  
DISCHARGE  
AIR SENSOR  
OPTIONAL  
OUTDOOR  
AIR SENSOR  
OPTIONAL  
OUTDOOR  
AIR SENSOR  
icomfort Touch®  
THERMOSTAT  
icomfort Touch®  
THERMOSTAT  
icomfortt− ENABLED  
OUTDOOR AIR CONDITIONING  
OR HEAT PUMP UNIT  
NON−COMMUNICATING  
OUTDOOR AIR  
CONDITIONING UNIT −  
1 OR 2 STAGE  
CLIP ON−BOARD LINK  
W915 (Y1 TO Y2) FOR  
TWO−STAGE OPERATION  
NOTE − On communicating systems, extra wires must terminate on the "C" icomfortt terminal strip (RSBus). Use an additional wire  
and come off "C" terminal and wire nut all the extra wires together. Termination on the outdoor control must match the indoor control.  
icomfortt Integrated Control  
Outdoor Unit  
®
icomfort Touch  
FIGURE 30  
Page 27  
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®
Optional Accessories for use with any icomfort Touch System  
®
NOTE: icomfort Touch THERMOSTAT SENSES HUMIDITY  
& CONTROLS HUM CONTACTS TO CYCLE HUMIDIFIER  
BASED ON DEMAND. NO OTHER CONTROL OR HUMIDIS-  
TAT REQUIRED.  
120V CONNECTIONS  
ꢀHUM" CONTACT IS  
CLOSED ANYTIME  
HUMIDITY DEMAND  
IS PRESENT  
OPTIONAL OUTDOOR AIR SENSOR FOR USE WITH HU-  
MIDIFIER (IF NOT ALREADY IN THE SYSTEM FOR OTHER  
FUNCTIONS. BUILT INTO ALL icomfort by Lennoxt OUT-  
DOOR UNITS).  
icomfortt ENABLED  
SL280UHV FURNACE  
24V HUMIDIFIER CONNECTIONS  
Discharge Air  
Sensor (Required  
for even heat)  
CS 7000  
THERMOSTAT  
®
icomfort Touch  
THERMOSTAT  
CONVENTIONAL  
NON−COMMUNI-  
CATING SYSTEM  
RSBus  
Maximum total  
COMMUNICATING SYSTEM  
length of all con-  
nections on the  
RSBus is limited  
to 1500ft.  
*24V IN jumper not used in non−  
communicating configuration  
Wire gauge of  
RSBus wire is 18.  
*24V IN  
JUMPER  
icomfortt ENABLED  
SL280UHV FURNACE  
NOTE: 24V UV LIGHT  
APPLICATIONS  
In an icomfort by Lennoxt system,  
neither furnace nor air handler trans-  
former will have adequate VA to  
power 24V UV light applications. An  
additional transformer for UV light  
applications is required.  
®
icomfort Touch  
THERMOSTAT  
icomfort  
t
ENABLED OUTDOOR  
AIR CONDITIONING OR  
HEAT PUMP UNIT  
DEHUMIDIFIER  
CONTROL  
(POWER COMPANY INTERRUPTION SYSTEMS  
ARE WIRED SAME AS OVERFLOW SWITCH)  
HVAC  
EQUIPMENT  
HEPA BYPASS FILTER X2680 HEPA INTERLOCK KIT  
STANDARD 1 OR 2  
STAGE AC OR HP UNIT  
PASS INDOOR BLOWER  
MOTOR COMMON WIRE  
THROUGH CURRENT LOOP.  
NON−COMMUNICATING  
SYSTEM WIRING  
SEE HEPA INTERLOCK KIT  
FOR INSTALLATION DE-  
TAILS  
LVCS VENTILATION CONTROL SYSTEM  
SEE LVCS VENTILATION  
INSTRUCTIONS FOR  
DAMPER & SENSOR WIRING  
2 STAGE FURNACE  
DS  
COMMUNICATING  
SYSTEM WIRING  
CUT  
R−DS  
W914  
R
FIGURE 31  
Page 28  
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TABLE 11  
SL280 Field Wiring Applications With Conventional Thermostat  
DIP Switch Settings and On−Board Links (See figure 34)  
DIP Switch 1  
On Board Links Must Be Cut To Select  
System Options  
Thermostat  
Heating  
Stages  
Thermostat  
Wiring Connections  
1 Heat / 1 Cool  
ON  
ON  
ON  
S1  
T’STAT  
FURNACE  
TERM. STRIP  
OUTDOOR  
UNIT  
NOTE − Use DIP  
switch 2 to set  
second−stage  
heat ON delay.  
OFF−7 minutes.  
ON−12 minutes.  
DO NOT CUT ANY  
ON−BOARD LINKS  
*
1 Heat / 2 Cool  
S1  
T’STAT  
FURNACE  
TERM. STRIP  
OUTDOOR  
UNIT  
NOTE − Use DIP  
switch 2 to set  
second−stage  
heat ON delay.  
OFF−7 minutes.  
ON−12 minutes.  
CUT ON−BOARD LINK  
W915  
2 STAGE  
*
COMPR  
1 Heat / 2 Cool  
with t’stat with  
humidity control  
S1  
T’STAT  
FURNACE  
TERM. STRIP  
OUTDOOR  
UNIT  
CUT ON−BOARD LINK  
W915  
2 STAGE  
COMPR  
NOTE − Use DIP  
switch 2 to set  
second−stage  
*
heat ON delay.  
OFF−7 minutes.  
ON−12 minutes.  
CUT ON−BOARD LINK  
W914  
DEHUM  
OR  
HARMONY  
o
* Not required on all units.  
Page 29  
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TABLE 11  
SL280 Field Wiring Applications With Conventional Thermostat (Continued)  
DIP Switch Settings and On−Board Links (See figure 34)  
DIP Switch 1  
On Board Links Must Be Cut To Select  
System Options  
Thermostat  
Heating  
Stages  
Thermostat  
Wiring Connections  
2 Heat / 2 Cool  
OFF  
OFF  
OFF  
OFF  
S1  
T’STAT  
FURNACE  
TERM. STRIP  
OUTDOOR  
UNIT  
CUT ON−BOARD LINK  
W915  
2 STAGE  
COMPR  
*
2 Heat / 2 Cool  
with t’stat with  
humidity control  
S1  
T’STAT  
FURNACE  
TERM. STRIP  
OUTDOOR  
UNIT  
CUT ON−BOARD LINK  
W915  
2 STAGE  
COMPR  
*
CUT ON−BOARD LINK  
W914  
DEHUM  
OR  
HARMONY  
o
2 Heat / 1 Cool  
with t’stat with  
humidity control  
S1  
T’STAT  
FURNACE  
TERM. STRIP  
OUTDOOR  
UNIT  
CUT ON−BOARD LINK  
W914  
DEHUM  
OR  
*
HARMONY  
o
2 Heat / 1 Cool  
S1  
T’STAT  
FURNACE  
TERM. STRIP  
OUTDOOR  
UNIT  
DO NOT CUT ANY  
ON−BOARD LINKS  
*
* Not required on all units.  
Page 30  
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TABLE 11  
SL280 Field Wiring Applications With Conventional Thermostat (Continued)  
DIP Switch Settings and On−Board Links (figure 34)  
DIP Switch 1  
Wiring Connections  
Thermostat  
Heating  
Stages  
On Board Links Must Be Cut To Select  
System Options  
Thermostat  
FURNACE  
TERM. STRIP  
HEAT PUMP  
Dual Fuel  
Single Stage  
Heat Pump  
L7724U  
T’STAT  
OFF  
H
CUT ON−BOARD LINK  
W951  
HEAT  
PUMP  
ComfortSense  
7000 L7724U  
thermostat w/  
dual fuel capa-  
bilities  
67M41*  
L
Y
L
Capable of 2  
stage gas heat  
control  
Y2  
D
B
Y2  
T
T
outdoor  
sensor  
L7724U  
T’STAT  
FURNACE  
TERM. STRIP  
Dual Fuel  
Two Stage  
Heat Pump  
HEAT PUMP  
OFF  
CUT ON−BOARD LINK  
W915  
2 STAGE  
H
COMPR  
67M41*  
ComfortSense  
7000 L7724U  
thermostat w/  
dual fuel capa-  
bilities  
Capable of 2  
stage gas heat  
control  
CUT ON−BOARD LINK  
W951  
HEAT  
PUMP  
L
L
Y2  
Y2  
D
B
out blue  
T
T
outdoor  
sensor  
* Connect W1 to W1 ONLY if using defrost tempering kit 67M41  
NOTE − Do NOT make a wire connection between the room thermostat L terminal and the L terminal of the SL280  
integrated control.  
Page 31  
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TABLE 11  
SL280 Field Wiring Applications With Conventional Thermostat (Continued)  
DIP Switch Settings and On−Board Links (figure 34)  
DIP Switch 1  
Wiring Connections  
Thermostat  
Heating  
Stages  
On Board Links Must Be Cut To Select  
System Options  
Thermostat  
FURNACE  
TERM. STRIP  
HEAT PUMP  
Dual Fuel  
Single Stage  
Heat Pump  
L7724U  
T’STAT  
OFF  
H
CUT ON−BOARD LINK  
W951  
HEAT  
PUMP  
ComfortSense  
7000 L7724U  
thermostat w/  
dual fuel capa-  
bilities  
Capable of 2  
stage gas heat  
control w/dehu-  
midification  
control  
67M41*  
L
Y
L
CUT ON−BOARD LINK  
W914  
DEHUM  
OR  
Y2  
HARMONY  
D
B
Y2  
T
T
outdoor  
sensor  
FURNACE  
TERM. STRIP  
HEAT PUMP  
Dual Fuel  
Two Stage  
Heat Pump  
L7724U  
T’STAT  
CUT ON−BOARD LINK  
W915  
2 STAGE  
OFF  
COMPR  
H
ComfortSense  
7000 L7724U  
thermostat w/  
dual fuel capa-  
bilities  
Capable of 2  
stage gas heat  
control w/dehu-  
midification  
67M41*  
CUT ON−BOARD LINK  
W951  
HEAT  
PUMP  
L
L
CUT ON−BOARD LINK  
W914  
DEHUM  
OR  
Y2  
Y2  
HARMONY  
D
B
Y2  
out blue  
T
T
outdoor  
sensor  
* Connect W1 to W1 ONLY if using defrost tempering kit 67M41  
NOTE − Do NOT make a wire connection between the room thermostat L terminal and the L terminal of the SL280  
integrated control.  
Page 32  
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SL280UHV Schematic Wiring Diagram  
FIGURE 32  
Page 33  
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TYPICAL SL280UHV FIELD WIRING DIAGRAM  
FIELD INSTALLED CLASS II 24V  
FIELD INSTALLED LINE VOLTAGE  
FIGURE 33  
Page 34  
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Integrated Control  
ACC  
HUM  
HS/ CAI  
LINE 1  
NEUTRAL  
7 SEGMENT LED  
FLAME SENSE  
INDOOR  
BLOWER  
CONNECTOR  
DIAGNOSTIC  
PUSH BUTTON  
DIP SWITCHES  
12 PIN LOW  
VOLTAGE  
CONNECTOR  
OUTDOOR AIR  
SENSOR  
TERMINALS  
DISCHARGE AIR  
SENSOR  
TERMINALS  
W915 Y1 TO Y2  
2 STAGE COMPR  
W951 R TO O  
HEAT PUMP  
TB83  
COMMUNICATING  
OUTDOOR  
EQUIPMENT  
W914 R TO DS  
DEHUM OR  
HARMONY  
I + I −  
I + I −  
R
C
R
C
C
C
TB84  
W1 W2  
G
Y1  
R
DH  
L
O
DS  
Y2  
COMMUNICATING  
INDOOR  
THERMOSTAT  
NON−COMMUNICATINGNG  
24V TERMINALS  
RS−BUS LINK (TB82, future use)  
THERMOSTAT CONNECTIONS (TB1)  
DS = DEHUMIDIFICATION SIGNAL  
I+ = DATA HIGH CONNECTION  
I − = DATA LOW CONNECTION  
W2 = HEAT DEMAND FROM 2ND STAGE T/STAT  
W1 = HEAT DEMAND FROM 1ST STAGE T/STAT  
R = CLASS 2 VOLTAGE TO THERMOSTAT  
G = MANUAL FAN FROM T’STAT  
RS−BUS OUTDOOR (TB83)  
R = 24VAC  
I + = DATA HIGH CONNECTION  
I − = DATA LOW CONNECTION  
C = 24VAXC COMMON  
C = THERMOSTAT SIGNAL GROUND CONNECTED TO  
TRANSFORMER GRD (TR) & CHASIS GROUND (GRD)  
RS−BUS INDOOR (TB84)  
Y1 = THERMOSTAT 1ST STAGE COOL SIGNAL  
Y2 = THERMOSTAT 2ND STAGE COOL SIGNAL  
R = 24VAC  
I + = DATA HIGH CONNECTION  
I − = DATA LOW CONNECTION  
C = 24VAXC COMMON  
O = THERMOSTAT SIGNAL TO HEAT PUMP  
REVERSING VALVE  
1/4" QUICK CONNECT TERMINALS  
DH = DEHUMIDIFICATION OUTPUT COMMUNICATING  
THERMOSTAT ONLY  
HUM = UNPOWERED NORMALLY OPEN (DRY) CONTACTS  
XMFR = 120 VAC OUTPUT TO TRANSFORMER  
LI = 120 VAC INPUT TO CONTROL  
L = USE ONLY WITH A COMMUNICATING THERMOSTAT  
AND A NON−COMMUNICATING OUTDOOR UNIT  
ACC = 120 VAC OUTPUT TO OPTIONAL ACCESSORY  
NEUTRALS = 120 VAC NEUTRAL  
FIGURE 34  
. . . . . . . . . . . . .  
Page 35  
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settings provide lower supply air temperatures; shorter set-  
tings provide higher supply air temperatures.Table 12 pro-  
vides the blower off timings that will result from different  
switch settings.  
Integrated Control DIP Switch Settings −  
Conventional Thermostat (non−communi-  
cating)  
TABLE 12  
Blower Off Delay Switch Settings  
SL280UHV units are equipped with a two−stage, variable  
speed integrated control. This control manages ignition  
timing, heating mode fan off delays and indoor blower  
speeds based on selections made using the control dip  
switches and jumpers. The control includes an internal  
watchguard feature which automatically resets the ignition  
control when it has been locked out. After one hour of con-  
tinuous thermostat demand for heat, the watchguard will  
break and remake thermostat demand to the furnace and  
automatically reset the control to relight the furnace.  
Blower Off Delay  
(Seconds)  
60  
Switch 3  
Switch 4  
On  
Off  
Off  
On  
Off  
Off  
On  
On  
90 (Factory)  
120  
180  
Indoor Blower Operation DIP Switch Settings  
®
Switches 5 and 6 −− Cooling Mode Blower Speed −− The  
unit is shipped from the factory with the dip switches posi-  
tioned for high speed (4) indoor blower motor operation  
during the cooling mode. Table 13 provides the cooling  
mode blower speeds that will result from different switch  
settings. Switches 5 and 6 set the blower cfm for second−  
stage cool. The integrated control automatically ramps  
down to 70% of the second−stage cfm for first−stage cfm.  
Refer to tables for corresponding cfm values.  
Note: All icomfortt settings are set at the icomfort Touch  
thermostat. See icomfortt installation instruction. In icom-  
fortt communication system all DIP switch and clippable  
link settings are ignored. For conventional thermostats pro-  
ceed with DIP switch and clippable link settings as outlined  
in the following.  
Heating Operation DIP Switch Settings  
Switch 1 −− Thermostat Selection −− This unit may be used  
with either a single−stage or two−stage thermostat. The  
thermostat selection is made using a DIP switch which  
must be properly positioned for the particular application.  
The DIP switch is factory−positioned for use with a two−  
stage thermostat. If a single−stage thermostat is to be used,  
the DIP switch must be repositioned.  
TABLE 13  
Cooling Mode Blower Speeds  
Speed  
Low  
Switch 5  
On  
Switch 6  
On  
Medium Low  
Medium High  
High (Factory)  
Off  
On  
On  
Off  
Select ꢀOFF" for two−stage heating operation con-  
trolled by a two−stage heating thermostat (factory set-  
ting);  
Off  
Off  
Switches 7 and 8 −− Cooling Blower Speed Adjustment  
−− The unit is shipped from the factory with the dip switches  
positioned for NORMAL (no) adjustment. The dip switches  
may be positioned to adjust the blower speed by +10% or  
−10% to better suit the application. Table 14 below provides  
blower speed adjustments that will result from different  
switch settings. Refer to tables for corresponding cfm val-  
ues.  
b − Select ꢀON" for two−stage heating operation con-  
trolled by a single−stage heating thermostat. This set-  
ting provides a timed delay before second−stage heat  
is initiated.  
Switch 2 −− Second Stage Delay (Used with Single−  
Stage Thermostat Only) −− This switch is used to deter-  
mine the second stage on delay when a single−stage ther-  
mostat is being used. The switch is factory−set in the OFF  
position, which provides a 7−minute delay before second−  
stage heat is initiated. If the switch is toggled to the ON  
position, it will provide a 12−minute delay before second−  
stage heat is initiated. This switch is only activated when  
the thermostat selector jumper is positioned for SINGLE−  
stage thermostat use.  
TABLE 14  
Cooling Blower Speed Adjustment  
Adjustment  
+10% (approx.)  
Factory Default  
−10% (approx.)  
Switch 7  
On  
Switch 8  
Off  
Off  
Off  
Off  
On  
Switches 9 and 10 −− Cooling Mode Blower Speed  
Ramping −− Blower speed ramping may be used to en-  
hance dehumidification performance. The switches are  
factory set at option A which has the greatest effect on de−  
humidification performance. Table 15 provides the cooling  
mode blower speed ramping options that will result from  
different switch settings. The cooling mode blower speed  
ramping options are detailed on the next page.  
Switches 3 and 4 −− Blower−Off Delay −− The blower−on  
delay of 30 seconds is not adjustable. The blower−off delay  
(time that the blower operates after the heating demand  
has been satisfied) can be adjusted by moving switches 3  
and 4 on the integrated control. The unit is shipped from the  
factory with a blower−off delay of 90 seconds. The blower  
off delay affects comfort and is adjustable to satisfy individ-  
ual applications. Adjust the blower off delay to achieve a  
supply air temperature between 90° and 110°F at the exact  
moment that the blower is de−energized. Longer off delay  
NOTE − The off portion of the selected ramp profile also ap-  
plies during heat pump operation in dual fuel applications.  
Page 36  
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TABLE 15  
Cooling Mode Blower Speed Ramping  
Ramping Option D  
S
Motor runs at 100% until demand is satisfied.  
Ramping Option  
Switch 9  
Off  
Switch 10  
S
Once demand is met, motor ramps down to stop.  
A (Factory)  
Off  
On  
Off  
On  
B
C
D
Off  
100% CFM  
On  
OFF  
OFF  
COMPRESSOR  
DEMAND  
On  
Ramping Option A (Factory Selection)  
D Motor runs at 50% for 30 seconds.  
Switches 11, 12 and 13 −− Heating Mode Blower Speed −−  
The switches are factory set to the OFF position which pro-  
vides factory default heat speed. Refer to table 16 for  
switches 11, 12 and 13 that provided the corresponding in-  
creases or decrease to both high and low heat demand.  
D Motor then runs at 82% for approximately 7−1/2 minu-  
tes.  
D If demand has not been satisfied after 7−1/2 minutes,  
motor runs at 100% until demand is satisfied.  
D Once demand is met, motor runs at 50% for 30 sec-  
onds then ramps down to stop.  
TABLE 16  
Heating Mode Blower Speeds  
Switch  
11  
Switch  
12  
Switch  
13  
Heat Speed  
7 1/2 MIN  
82% CFM  
100%  
CFM  
OFF  
Increase 24%  
Increase 18%  
Increase 12%  
Increase 6%  
On  
On  
On  
On  
Off  
Off  
Off  
Off  
On  
On  
Off  
Off  
Off  
Off  
On  
On  
On  
Off  
On  
Off  
Off  
On  
Off  
On  
OFF  
1/2 MIN  
50% CFM  
1/2 MIN  
50% CFM  
COMPRESSOR DEMAND  
Factory Default  
Decrease 6%  
Decrease 12%  
Decrease18%  
Ramping Option B  
S
S
Motor runs at 82% for approximately 7−1/2 minutes. If  
demand has not been satisfied after 7−1/2 minutes,  
motor runs at 100% until demand is satisfied.  
Once demand is met, motor ramps down to stop.  
Switches 14 and 15 −− Continuous Blower Speed −−  
Table 17 provides continuous blower speed adjustments  
that will result from different switch settings.  
7 1/2 MIN  
82%CFM  
100% CFM  
OFF  
OFF  
COMPRESSOR DEMAND  
TABLE 17  
Continuous Blower Speed  
Continuous  
Switch 14 Switch 15  
Blower Speed  
Ramping Option C  
S
S
Motor runs at 100% until demand is satisfied.  
28% of High Cool Speed  
Off  
Off  
On  
Off  
Once demand is met, motor runs at 100% for 45 sec-  
onds then ramps down to stop.  
38% of High Cool Speed  
(Factory)  
70% of High Cool Speed  
100% of High Cool Speed  
On  
On  
Off  
On  
100% CFM  
100% CFM  
45 SEC.  
OFF  
OFF  
COMPRESSOR  
DEMAND  
Page 37  
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On−Board Link W915 2 Stage Compr (Y1 to Y2)  
On−board link W915 is a clippable connection between ter-  
minals Y1 and Y2 on the integrated control. W915 must be  
cut if two−stage cooling will be used. If the Y1 to Y2 link is  
not cut the outdoor unit will operate in second−stage cooling  
only.  
On−Board Links  
Note: In icomfortt systems with a conventional outdoor  
unit (non−communicating), the on−board clippable links  
must be set to properly configure the system.  
Diagnostic LED (Figure 34)  
The seven−segment diagnostic LED displays operating  
status, target airflow, error codes and other information.  
The table beginning on Page 60 lists diagnostic LED  
codes.  
WARNING  
Carefully review all configuration information pro-  
vided. Failure to properly set DIP switches, jumpers  
and on−board links can result in improper operation!  
Diagnostic Push Button (Figure 34)  
The diagnostic push button is located adjacent to the  
seven−segment diagnostic LED. This button is used to en-  
able the Error Code Recall ꢁE" mode and the Flame Signal  
ꢁF" mode. Press the button and hold it to cycle through a  
menu of options. Every five seconds a new menu item will  
be displayed. When the button is released, the displayed  
item will be selected. Once all items in the menu have been  
displayed, the menu resumes from the beginning until the  
button is released.  
On−Board Link W914 Dehum or Harmony (R to DS)  
On−board link W914, is a clippable connection between ter-  
minals R and DS on the integrated control. W914 must be  
cut when the furnace is installed with either the Harmony  
IIIt zone control or a thermostat which features humidity  
control. If the link is left intact the PMW signal from the Har-  
mony III control will be blocked and also lead to control  
damage. Refer to table 18 for operation sequence in ap-  
plications including SL280UHV, a thermostat which fea-  
tures humidity control and a single−speed outdoor unit.  
Table 19 gives the operation sequence in applications with  
a two−speed outdoor unit.  
Error Code Recall Mode  
Select "E" from the menu to access the most recent 10 error  
codes. Select ꢁc" from the Error Code Recall menu to clear  
all error codes. Button must be pressed a second time  
while ꢁc" is flashing to confirm command to delete codes.  
Press the button until a solid ꢁ≡" is displayed to exit the Error  
Code Recall mode.  
On−Board Link W951 Heat Pump (R to O)  
On−board link W951 is a clippable connection between ter-  
minals R and O on the integrated control. W951 must be cut  
when the furnace is installed in applications which include a  
heat pump unit and a thermostat which features dual fuel  
use. If the link is left intact, terminal ꢁO" will remain ener-  
gized eliminating the HEAT MODE in the heat pump.  
Flame Signal Mode  
Select "F" from the menu to access the flame signal mode.  
The integrated control will display the flame current on 7  
segment LED in in micro amps (uA).  
Flame signal mode is exited after the following:  
D
P
o
w
e
r
i
s
r
e
s
e
t
D Pressing and holding push button until 3 horizontal  
lines ꢁ≡" are displayed  
D 10 minutes of entering the flame sense mode.  
Page 38  
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BLOWER DATA  
SL280UH070V36A BLOWER PERFORMANCE (less filter)  
BOTTOM RETURN AIR  
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range  
HEATING  
1 Heating Speed  
DIP Switch  
Settings  
First Stage Heating Speed - cfm  
Second Stage Heating Speed - cfm  
+24%  
+18%  
1045  
985  
940  
880  
850  
785  
745  
680  
1145  
1080  
1035  
960  
+12%  
+6%  
Factory Default  
–6%  
925  
875  
–12%  
815  
–18%  
745  
COOLING  
1 Cooling Speed  
DIP Switch  
Settings  
First Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Second Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Low  
2 High  
Low  
2 High  
+
781  
695  
645  
819  
734  
674  
872  
797  
720  
981  
883  
815  
1045  
943  
1139  
1005  
922  
1219  
1114  
991  
1372  
1260  
1144  
Factory Default  
–
847  
SINGLE SIDE RETURN AIR  
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range  
HEATING  
1 Heating Speed  
DIP Switch  
Settings  
First Stage Heating Speed - cfm  
Second Stage Heating Speed - cfm  
+24%  
+18%  
1050  
1000  
940  
895  
820  
775  
735  
685  
1165  
1110  
1040  
975  
+12%  
+6%  
Factory Default  
–6%  
935  
855  
–12%  
805  
–18%  
750  
COOLING  
1 Cooling Speed  
DIP Switch  
Settings  
First Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Second Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Low  
2 High  
Low  
2 High  
+
764  
704  
642  
802  
725  
680  
886  
793  
717  
977  
899  
812  
1035  
949  
1122  
1029  
933  
1248  
1135  
1021  
1360  
1257  
1133  
Factory Default  
–
874  
1 Cooling and heating speeds are based on a combination of DIP switch settings on the furnace control. Refer to Installation Instructions for specific DIP Switch  
Settings.  
2 Factory default setting.  
NOTES - The effect of static pressure is included in air volumes shown.  
First stage HEAT is approximately 91% of the same second stage HEAT.  
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.  
Continuous Fan Only speed is selectable at 28%, 38%, 70% and 100% of the selected second stage cooling speed - minimum 500 cfm.  
Lennox Harmony III™ Zone Control Applications - Minimum blower speed is 425 cfm.  
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BLOWER DATA  
SL280UH090V36B BLOWER PERFORMANCE (less filter)  
BOTTOM RETURN AIR  
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range  
HEATING  
1 Heating Speed  
DIP Switch  
Settings  
First Stage Heating Speed - cfm  
Second Stage Heating Speed - cfm  
+24%  
+18%  
1300  
1250  
1185  
1145  
1070  
1015  
970  
1420  
1335  
1285  
1240  
1170  
1100  
1035  
980  
+12%  
+6%  
Factory Default  
–6%  
–12%  
–18%  
880  
COOLING  
1 Cooling Speed  
DIP Switch  
Settings  
First Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Second Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Low  
2 High  
Low  
2 High  
+
616  
571  
489  
755  
698  
627  
846  
767  
681  
980  
886  
812  
1018  
909  
1197  
1083  
968  
1291  
1197  
1081  
1399  
1284  
1179  
Factory Default  
–
834  
SINGLE SIDE RETURN AIR  
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range  
HEATING  
1 Heating Speed  
DIP Switch  
Settings  
First Stage Heating Speed - cfm  
Second Stage Heating Speed - cfm  
+24%  
+18%  
1305  
1250  
1195  
1135  
1070  
995  
1425  
1350  
1290  
1230  
1165  
1100  
1030  
960  
+12%  
+6%  
Factory Default  
–6%  
–12%  
935  
–18%  
870  
COOLING  
1 Cooling Speed  
DIP Switch  
Settings  
First Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Second Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Low  
2 High  
Low  
2 High  
+
611  
575  
519  
731  
674  
604  
830  
748  
691  
971  
870  
786  
995  
889  
808  
1160  
1075  
952  
1274  
1160  
1056  
1376  
1270  
1147  
Factory Default  
–
1 Cooling and heating speeds are based on a combination of DIP switch settings on the furnace control. Refer to Installation Instructions for specific DIP Switch  
Settings.  
2 Factory default setting.  
NOTES - The effect of static pressure is included in air volumes shown.  
First stage HEAT is approximately 91% of the same second stage HEAT.  
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.  
Continuous Fan Only speed is selectable at 28%, 38%, 70% and 100% of the selected second stage cooling speed - minimum 500 cfm.  
Lennox Harmony III™ Zone Control Applications - Minimum blower speed is 455 cfm.  
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BLOWER DATA  
SL280UH090V48B BLOWER PERFORMANCE (less filter)  
BOTTOM RETURN AIR  
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range  
HEATING  
1 Heating Speed  
DIP Switch  
Settings  
First Stage Heating Speed - cfm  
Second Stage Heating Speed - cfm  
+24%  
+18%  
1280  
1220  
1155  
1095  
1035  
970  
1410  
1340  
1270  
1205  
1135  
1070  
1000  
930  
+12%  
+6%  
Factory Default  
–6%  
–12%  
910  
–18%  
845  
COOLING  
1 Cooling Speed  
DIP Switch  
Settings  
First Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Second Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Low  
2 High  
Low  
2 High  
+
670  
605  
525  
890  
815  
690  
1040  
965  
1210  
1090  
985  
1030  
940  
1335  
1205  
1060  
1550  
1405  
1260  
1755  
1,600  
1435  
Factory Default  
–
850  
795  
SINGLE SIDE RETURN AIR  
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range  
HEATING  
1 Heating Speed  
DIP Switch  
Settings  
First Stage Heating Speed - cfm  
Second Stage Heating Speed - cfm  
+24%  
+18%  
1280  
1220  
1155  
1095  
1035  
970  
1410  
1340  
1270  
1205  
1135  
1070  
1000  
930  
+12%  
+6%  
Factory Default  
–6%  
–12%  
910  
–18%  
845  
COOLING  
1 Cooling Speed  
DIP Switch  
Settings  
First Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Second Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Low  
2 High  
Low  
2 High  
+
640  
570  
530  
900  
780  
700  
1015  
930  
1175  
1040  
955  
1005  
895  
1295  
1160  
1050  
1500  
1345  
1210  
1670  
1500  
1405  
Factory Default  
–
810  
795  
1 Cooling and heating speeds are based on a combination of DIP switch settings on the furnace control. Refer to Installation Instructions for specific DIP Switch  
Settings.  
2 Factory default setting.  
NOTES - The effect of static pressure is included in air volumes shown.  
First stage HEAT is approximately 91% of the same second stage HEAT.  
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.  
Continuous Fan Only speed is selectable at 28%, 38%, 70% and 100% of the selected second stage cooling speed - minimum 500 cfm.  
Lennox Harmony III™ Zone Control Applications - Minimum blower speed is 455 cfm.  
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BLOWER DATA  
SL280UH090V48B BLOWER PERFORMANCE (less filter)  
SIDE RETURN AIR WITH OPTIONAL RETURN AIR BASE  
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range  
HEATING  
1 Heating Speed  
DIP Switch  
Settings  
First Stage Heating Speed - cfm  
Second Stage Heating Speed - cfm  
+24%  
+18%  
1295  
1235  
1170  
1110  
1045  
980  
1425  
1355  
1290  
1220  
1150  
1080  
1010  
945  
+12%  
+6%  
Factory Default  
–6%  
–12%  
920  
–18%  
855  
COOLING  
1 Cooling Speed  
DIP Switch  
Settings  
First Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Second Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Low  
2 High  
Low  
2 High  
+
660  
600  
535  
905  
760  
700  
1030  
930  
1175  
1045  
970  
985  
905  
815  
1290  
1125  
1040  
1495  
1345  
1225  
1675  
1525  
1385  
Factory Default  
–
850  
1 Cooling and heating speeds are based on a combination of DIP switch settings on the furnace control. Refer to Installation Instructions for specific DIP Switch  
Settings.  
2 Factory default setting.  
NOTES - The effect of static pressure is included in air volumes shown.  
First stage HEAT is approximately 91% of the same second stage HEAT.  
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.  
Continuous Fan Only speed is selectable at 28%, 38%, 70% and 100% of the selected second stage cooling speed - minimum 500 cfm.  
Lennox Harmony III™ Zone Control Applications - Minimum blower speed is 455 cfm.  
Download from Www.SomanPuaaglse.co4m2. All Manuals Search And Download.  
BLOWER DATA  
SL280UH090V60C BLOWER PERFORMANCE (less filter)  
BOTTOM RETURN AIR, RETURN AIR FROM BOTH SIDES OR RETURN AIR FROM BOTTOM AND ONE SIDE  
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range  
HEATING  
1 Heating Speed  
DIP Switch  
Settings  
First Stage Heating Speed - cfm  
Second Stage Heating Speed - cfm  
+24%  
+18%  
1420  
1355  
1285  
1215  
1145  
1080  
1010  
940  
1565  
1490  
1415  
1335  
1260  
1185  
1110  
1035  
+12%  
+6%  
Factory Default  
–6%  
–12%  
–18%  
COOLING  
1 Cooling Speed  
DIP Switch  
Settings  
First Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Second Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Low  
2 High  
Low  
2 High  
+
1110  
1005  
890  
1205  
1100  
1015  
1420  
1280  
1125  
1680  
1545  
1380  
1575  
1440  
1295  
1740  
1595  
1450  
2000  
1820  
1610  
2305  
2125  
1930  
Factory Default  
–
SINGLE SIDE RETURN AIR  
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range  
HEATING  
1 Heating Speed  
DIP Switch  
Settings  
First Stage Heating Speed - cfm  
Second Stage Heating Speed - cfm  
+24%  
+18%  
1360  
1295  
1230  
1165  
1100  
1030  
965  
1500  
1425  
1355  
1280  
1210  
1135  
1065  
990  
+12%  
+6%  
Factory Default  
–6%  
–12%  
–18%  
900  
COOLING  
1 Cooling Speed  
DIP Switch  
Settings  
First Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Second Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Low  
2 High  
Low  
2 High  
+
1050  
955  
1165  
1060  
945  
1335  
1215  
1090  
1620  
1480  
1290  
1515  
1390  
1220  
1680  
1545  
1385  
1915  
1735  
1580  
2225  
2060  
1825  
Factory Default  
–
840  
1 Cooling and heating speeds are based on a combination of DIP switch settings on the furnace control. Refer to Installation Instructions for specific DIP Switch  
Settings.  
2 Factory default setting.  
NOTES - The effect of static pressure is included in air volumes shown.  
First stage HEAT is approximately 91% of the same second stage HEAT.  
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.  
Continuous Fan Only speed is selectable at 28%, 38%, 70% and 100% of the selected second stage cooling speed - minimum 500 cfm.  
Lennox Harmony III™ Zone Control Applications - Minimum blower speed is 480 cfm.  
Download from Www.Somanuals.coPma. Aglel M4a3nuals Search And Download.  
BLOWER DATA  
SL280UH090V60C BLOWER PERFORMANCE (less filter)  
SIDE RETURN AIR WITH OPTIONAL RETURN AIR BASE  
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range  
HEATING  
1 Heating Speed  
DIP Switch  
Settings  
First Stage Heating Speed - cfm  
Second Stage Heating Speed - cfm  
+24%  
+18%  
1360  
1290  
1225  
1160  
1095  
1030  
965  
1495  
1420  
1350  
1275  
1205  
1130  
1060  
990  
+12%  
+6%  
Factory Default  
–6%  
–12%  
–18%  
900  
COOLING  
1 Cooling Speed  
DIP Switch  
Settings  
First Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Second Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Low  
2 High  
Low  
2 High  
+
1050  
970  
1190  
1090  
985  
1380  
1245  
1095  
1615  
1485  
1285  
1515  
1380  
1215  
1715  
1560  
1400  
1930  
1755  
1580  
2240  
2070  
1830  
Factory Default  
–
880  
1 Cooling and heating speeds are based on a combination of DIP switch settings on the furnace control. Refer to Installation Instructions for specific DIP Switch  
Settings.  
2 Factory default setting.  
NOTES - The effect of static pressure is included in air volumes shown.  
First stage HEAT is approximately 91% of the same second stage HEAT.  
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.  
Continuous Fan Only speed is selectable at 28%, 38%, 70% and 100% of the selected second stage cooling speed - minimum 500 cfm.  
Lennox Harmony III™ Zone Control Applications - Minimum blower speed is 480 cfm.  
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BLOWER DATA  
SL280UH110V60C BLOWER PERFORMANCE (less filter)  
BOTTOM RETURN AIR, RETURN AIR FROM BOTH SIDES OR RETURN AIR FROM BOTTOM AND ONE SIDE  
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range  
HEATING  
1 Heating Speed  
DIP Switch  
Settings  
First Stage Heating Speed - cfm  
Second Stage Heating Speed - cfm  
+24%  
+18%  
1690  
1605  
1525  
1445  
1360  
1280  
1200  
1115  
1855  
1765  
1675  
1585  
1495  
1405  
1315  
1230  
+12%  
+6%  
Factory Default  
–6%  
–12%  
–18%  
COOLING  
1 Cooling Speed  
DIP Switch  
Settings  
First Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Second Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Low  
2 High  
Low  
2 High  
+
1060  
970  
1220  
1075  
980  
1330  
1180  
1070  
1565  
1430  
1255  
1535  
1400  
1260  
1710  
1565  
1400  
1910  
1715  
1560  
2210  
2015  
1815  
Factory Default  
–
875  
SINGLE SIDE RETURN AIR  
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range  
HEATING  
1 Heating Speed  
DIP Switch  
Settings  
First Stage Heating Speed - cfm  
Second Stage Heating Speed - cfm  
+24%  
+18%  
1640  
1560  
1480  
1400  
1325  
1245  
1165  
1085  
1805  
1715  
1630  
1545  
1455  
1370  
1280  
1195  
+12%  
+6%  
Factory Default  
–6%  
–12%  
–18%  
COOLING  
1 Cooling Speed  
DIP Switch  
Settings  
First Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Second Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Low  
2 High  
Low  
2 High  
+
1020  
940  
1160  
1050  
945  
1285  
1155  
1020  
1550  
1400  
1250  
1505  
1375  
1235  
1690  
1525  
1380  
1855  
1685  
1505  
2125  
1935  
1730  
Factory Default  
–
835  
1 Cooling and heating speeds are based on a combination of DIP switch settings on the furnace control. Refer to Installation Instructions for specific DIP Switch  
Settings.  
2 Factory default setting.  
NOTES - The effect of static pressure is included in air volumes shown.  
First stage HEAT is approximately 91% of the same second stage HEAT.  
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.  
Continuous Fan Only speed is selectable at 28%, 38%, 70% and 100% of the selected second stage cooling speed - minimum 500 cfm.  
Lennox Harmony III™ Zone Control Applications - Minimum blower speed is 485 cfm.  
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BLOWER DATA  
SL280UH110V60C BLOWER PERFORMANCE (less filter)  
SIDE RETURN AIR WITH OPTIONAL RETURN AIR BASE  
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range  
HEATING  
1 Heating Speed  
DIP Switch  
Settings  
First Stage Heating Speed - cfm  
Second Stage Heating Speed - cfm  
+24%  
+18%  
1635  
1555  
1475  
1395  
1320  
1240  
1160  
1080  
1800  
1710  
1625  
1535  
1450  
1365  
1275  
1190  
+12%  
+6%  
Factory Default  
–6%  
–12%  
–18%  
COOLING  
1 Cooling Speed  
DIP Switch  
Settings  
First Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Second Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Low  
2 High  
Low  
2 High  
+
1085  
1010  
900  
1160  
1040  
955  
1270  
1160  
1025  
1490  
1375  
1205  
1595  
1470  
1315  
1660  
1535  
1365  
1840  
1655  
1510  
2115  
1940  
1735  
Factory Default  
–
1 Cooling and heating speeds are based on a combination of DIP switch settings on the furnace control. Refer to Installation Instructions for specific DIP Switch  
Settings.  
2 Factory default setting.  
NOTES - The effect of static pressure is included in air volumes shown.  
First stage HEAT is approximately 91% of the same second stage HEAT.  
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.  
Continuous Fan Only speed is selectable at 28%, 38%, 70% and 100% of the selected second stage cooling speed - minimum 500 cfm.  
Lennox Harmony III™ Zone Control Applications - Minimum blower speed is 485 cfm.  
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BLOWER DATA  
SL280UH135V60D BLOWER PERFORMANCE (less filter)  
BOTTOM RETURN AIR, RETURN AIR FROM BOTH SIDES OR RETURN AIR FROM BOTTOM AND ONE SIDE  
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range  
HEATING  
1 Heating Speed  
DIP Switch  
Settings  
First Stage Heating Speed - cfm  
Second Stage Heating Speed - cfm  
+24%  
+18%  
1875  
1785  
1695  
1605  
1515  
1425  
1330  
1240  
2065  
1965  
1865  
1765  
1665  
1565  
1465  
1365  
+12%  
+6%  
Factory Default  
–6%  
–12%  
–18%  
COOLING  
1 Cooling Speed  
DIP Switch  
Settings  
First Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Second Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Low  
2 High  
Low  
2 High  
+
1025  
965  
1120  
1015  
930  
1325  
1180  
1060  
1650  
1490  
1350  
1500  
1420  
1225  
1600  
1510  
1320  
1840  
1700  
1505  
2235  
2110  
1840  
Factory Default  
–
875  
SINGLE SIDE RETURN AIR  
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range  
HEATING  
1 Heating Speed  
DIP Switch  
Settings  
First Stage Heating Speed - cfm  
Second Stage Heating Speed - cfm  
+24%  
+18%  
1850  
1760  
1670  
1580  
1490  
1400  
1310  
1225  
2035  
1935  
1835  
1740  
1640  
1540  
1445  
1345  
+12%  
+6%  
Factory Default  
–6%  
–12%  
–18%  
COOLING  
1 Cooling Speed  
DIP Switch  
Settings  
First Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Second Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Low  
2 High  
Low  
2 High  
+
1030  
960  
1105  
1005  
925  
1305  
1175  
1050  
1635  
1480  
1340  
1525  
1355  
1240  
1600  
1435  
1315  
1840  
1635  
1520  
2255  
2035  
1850  
Factory Default  
–
845  
1 Cooling and heating speeds are based on a combination of DIP switch settings on the furnace control. Refer to Installation Instructions for specific DIP Switch  
Settings.  
2 Factory default setting.  
NOTES - The effect of static pressure is included in air volumes shown.  
First stage HEAT is approximately 91% of the same second stage HEAT.  
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.  
Continuous Fan Only speed is selectable at 28%, 38%, 70% and 100% of the selected second stage cooling speed - minimum 500 cfm.  
Lennox Harmony III™ Zone Control Applications - Minimum blower speed is 426 cfm.  
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BLOWER DATA  
SL280UH135V60D BLOWER PERFORMANCE (less filter)  
SIDE RETURN AIR WITH OPTIONAL RETURN AIR BASE  
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range  
HEATING  
1 Heating Speed  
DIP Switch  
Settings  
First Stage Heating Speed - cfm  
Second Stage Heating Speed - cfm  
+24%  
+18%  
1840  
1750  
1660  
1575  
1485  
1395  
1305  
1215  
2025  
1925  
1830  
1730  
1630  
1535  
1435  
1340  
+12%  
+6%  
Factory Default  
–6%  
–12%  
–18%  
COOLING  
1 Cooling Speed  
DIP Switch  
Settings  
First Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Second Stage Cooling Speed - cfm  
Medium-Low Medium-High  
Low  
2 High  
Low  
2 High  
+
1035  
955  
1105  
1005  
935  
1285  
1145  
1050  
1610  
1430  
1295  
1530  
1365  
1225  
1610  
1450  
1310  
1825  
1650  
1515  
2240  
2040  
1850  
Factory Default  
–
860  
1 Cooling and heating speeds are based on a combination of DIP switch settings on the furnace control. Refer to Installation Instructions for specific DIP Switch  
Settings.  
2 Factory default setting.  
NOTES - The effect of static pressure is included in air volumes shown.  
First stage HEAT is approximately 91% of the same second stage HEAT.  
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.  
Continuous Fan Only speed is selectable at 28%, 38%, 70% and 100% of the selected second stage cooling speed - minimum 500 cfm.  
Lennox Harmony III™ Zone Control Applications - Minimum blower speed is 495 cfm.  
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TABLE 18  
OPERATING SEQUENCE  
SL280UHV, Non−Communicating Thermostat with Humidity Control Feature and Single−Speed Outdoor Unit  
OPERATING  
SEQUENCE  
SYSTEM DEMAND  
Thermostat Demand Relative Humidity  
SYSTEM RESPONSE  
Blower  
CFM  
(COOL)  
System  
Condition  
Compres-  
sor  
Step  
Comments  
W
1
Y1  
O
G
Status  
D
NO CALL FOR DEHUMIDIFICATION  
Normal Operation On On On  
BASIC MODE (only active on a Y1 thermostat demand)  
Compressor and indoor  
blower follow thermostat  
demand  
24  
VAC  
1
Acceptable  
High  
100%  
24  
VAC  
®
ComfortSense 7000  
Normal Operation  
1
2
On On On  
On On On  
Acceptable  
Demand  
High  
High  
100%  
70%*  
thermostat energizes Y1  
and de−energizes D on a  
call for de−humidification  
Dehumidification  
Call  
0
VAC  
PRECISION MODE (operates independent of a Y1 thermostat demand)  
24  
VAC  
Normal Operation  
1
2
On On On  
On On On  
Acceptable  
Demand  
High  
High  
100%  
70%*  
Dehumidification mode  
begins when humidity is  
greater than set point  
Dehumidification  
call  
0
VAC  
®
ComfortSense 7000  
Dehumidification  
call ONLY  
0
VAC  
1
On On On  
Demand  
High  
70%*  
thermostat will try to  
maintain room humidity  
setpoint by allowing the  
room space to maintain a  
cooler room thermostat  
setpoint**  
Jumpers at indoor unit with a single stage outdoor unit  
With Condensing unit − Cut W914 (R to DS) on SureLight control  
With Heat Pump − Cut W914 (R to DS) & W951 (R to O) on SureLight control  
®
®
®
Dave Lennox ComfortSense 7000 thermostat to use for this application − Y2081 4 heat / 2 cool  
*Dehumidification blower speed is 70% of COOL speed for all units .  
®
**In Precision mode, ComfortSense 7000 thermostat will maintain room temperature up to 2 °F (1.2°C) cooler than room setting.  
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TABLE 19  
OPERATING SEQUENCE  
SL280UHV, Non−Communicating Thermostat with Humidity Control Feature and Two−Speed Outdoor Unit  
OPERATING  
SEQUENCE  
SYSTEM DEMAND  
Thermostat Demand Relative Humidity  
SYSTEM RESPONSE  
Blower  
CFM  
(COOL)  
System  
Condition  
Ste  
p
Compressor  
Comments  
W
1
W
2
Y1 Y2  
O
G
Status  
D
NO CALL FOR DEHUMIDIFICATION  
Normal Opera-  
tion − Y1  
24  
VAC  
1
2
On  
On On  
Acceptable  
Acceptable  
Low  
70%*  
100%  
Compressor and indoor  
blower follow thermostat  
demand  
Normal Opera-  
tion − Y2  
24  
VAC  
On On On On  
High  
ROOM THERMOSTAT CALLS FOR FIRST STAGE COOLING  
BASIC MODE (only active on a Y1 thermostat demand)  
Normal Opera-  
24  
VAC  
®
ComfortSense 7000  
1
On  
On On  
Acceptable  
Low  
70%*  
tion  
thermostat energizes Y2  
and de−energizes D on a  
call for de−humidification  
Dehumidification  
Call  
0
VAC  
2
On On On On  
Demand  
High  
70%**  
PRECISION MODE (operates independent of a Y1 thermostat demand)  
Normal Opera-  
tion  
24  
VAC  
1
2
On  
On On  
Acceptable  
Demand  
Low  
70%*  
Dehumidification mode  
begins when humidity is  
greater than set point  
Dehumidification  
call  
0
VAC  
On On On On  
High  
70%**  
®
ComfortSense 7000  
thermostat will try to  
maintain room humidity  
setpoint by allowing the  
room space to maintain a  
cooler room thermostat  
setpoint***  
Dehumidification  
call ONLY  
0
VAC  
1
On On On On  
Demand  
High  
70%**  
ROOM THERMOSTAT CALLS FOR FIRST AND SECOND STAGE COOLING  
BASIC MODE (only active on a Y1 thermostat demand)  
Normal Opera-  
tion  
24  
VAC  
®
ComfortSense 7000  
1
2
On On On On  
On On On On  
Acceptable  
Demand  
High  
High  
100%  
70%**  
thermostat energizes Y2  
and de−energizes D on a  
call for de−humidification  
Dehumidification  
Call  
0
VAC  
PRECISION MODE (operates independent of a Y1 thermostat demand)  
Normal Opera-  
tion  
24  
VAC  
1
2
On  
On On  
Acceptable  
Demand  
Low  
70%*  
Dehumidification mode  
begins when humidity is  
greater than set point  
Dehumidification  
call  
0
VAC  
On On On On  
On On On On  
High  
70%**  
®
ComfortSense 7000  
Dehumidification  
call ONLY  
0
VAC  
1
Demand  
High  
70%**  
thermostat will try to  
maintain room humidity  
setpoint by allowing the  
room space to maintain a  
cooler room thermostat  
setpoint***  
Jumpers at indoor unit with a two stage outdoor unit  
Cut factory jumper from Y1 to Y2 or cut W915 (Y1 to Y2)  
With Condensing unit − Cut W914 (R to DS) on SureLight control  
®
®
With Heat Pump − Cut W914 (R to DS) & W951 (R to O) on SureLight control  
®
Dave Lennox ComfortSense 7000 thermostat to use for this application − Y2081 4 heat / 2 cool  
*Normal operation first stage cooling blower speed is 70% COOL speed.  
**Dehumidification blower speed is, reduced to 70% of COOL.  
®
***In Precision mode, ComfortSense 7000 thermostat will maintain room temperature up to 2 °F (1.2°C) cooler than room setting.  
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2 − Set the thermostat to the lowest setting.  
3 − Turn off all electrical power to the unit.  
Unit Start−Up  
FOR YOUR SAFETY READ BEFORE LIGHTING  
4 − This furnace is equipped with an ignition device which  
automatically lights the burners. Do not try to light the  
burners by hand.  
WARNING  
5 − Remove the upper access panel.  
Do not use this furnace if any part has been underwa-  
ter. Immediately call a licensed professional service  
technician (or equivalent) to inspect the furnace and  
to replace any part of the control system and any gas  
control which has been under water.  
6−Move gas valve switch toOFF position. Do not force.  
See figure 35 or 36.  
7 − Wait five minutes to clear out any gas. If you then smell  
gas, STOP! Immediately call your gas supplier from a  
neighbor’s phone. Follow the gas supplier’s instruc-  
tions. If you do not smell gas go to next step.  
WARNING  
WHITE RODGERS GAS VALVE  
If overheating occurs or if gas supply fails to shut off,  
shut off the manual gas valve to the appliance before  
shutting off electrical supply.  
HIGH FIRE ADJUSTMENT  
SCREW  
(under cap)  
MANIFOLD  
PRESSURE TAP  
INLET PRESSURE POST  
CAUTION  
Before attempting to perform any service or mainte-  
nance, turn the electrical power to unit OFF at dis-  
connect switch.  
WARNING  
During blower operation, the ECM motor emits ener-  
gy that may interfere with pacemaker operation. In-  
terference is reduced by both the sheet metal cabinet  
and distance.  
GAS VALVE SHOWN IN ON POSITION  
FIGURE 35  
BEFORE LIGHTING smell all around the appliance area for  
gas. Be sure to smell next to the floor because some gas is  
heavier than air and will settle on the floor.  
HONEYWELL GAS VALVE  
HIGH FIRE  
ADJUSTING SCREW  
(under cap)  
INLET PRESSURE TAP  
ON SIDE  
The gas valve on the SL280UHV unit will be equipped with  
a gas control switch. Use only your hand to move the  
switch. Never use tools. If the switch will not turn or if the  
control switch will not move by hand, do not try to repair it.  
Placing the furnace into operation:  
SL280UHV units are equipped with an automatic ignition  
system. Do not attempt to manually light burners on these  
furnaces. Each time the thermostat calls for heat, the  
burners will automatically light. The ignitor does not get  
hot when there is no call for heat on units with an automatic  
ignition system.  
MANIFOLD  
PRESSURE  
TAP ON  
SIDE  
GAS VALVE SHOWN IN ON POSITION  
FIGURE 36  
WARNING  
8 − Move gas valve switch toON position. Do not force.  
See figure 35 or 36.  
If you do not follow these instructions exactly, a fire  
or explosion may result causing property damage,  
personal injury or death.  
9 − Replace the upper access panel.  
10− Turn on all electrical power to to the unit.  
11− Set the thermostat to desired setting.  
Gas Valve Operation (Figures 35 and 36)  
1 − STOP! Read the safety information at the beginning of  
NOTE − When unit is initially started, steps 1 through 11  
may need to be repeated to purge air from gas line.  
this section.  
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12− If the appliance will not operate, follow the instructions  
ꢁTurning Off Gas to Unit" and call your service techni-  
cian or gas supplier.  
TABLE 20  
GAS METER CLOCKING CHART  
Seconds for One Revolution  
Natural  
LP  
SL280  
Unit  
Turning Off Gas to Unit  
1 cu ft  
Dial  
2 cu ft  
Dial  
1 cu ft  
Dial  
2 cu ft  
DIAL  
1 − Set the thermostat to the lowest setting.  
2 − Turn off all electrical power to the unit if service is to be  
performed.  
−045  
−70  
80  
160  
110  
82  
200  
136  
102  
82  
400  
272  
204  
164  
136  
55  
3 − Remove the upper access panel.  
−90  
41  
4−Move gas valve switch toOFF position. Do not force.  
See figure 35 or 36.  
−110  
−135  
33  
66  
27  
54  
68  
5 − Replace the upper access panel.  
Natural−1000 btu/cu ft  
LP−2500 btu/cu ft  
Failure To Operate  
Supply Line Pressure  
If the unit fails to operate, check the following:  
1 − Is the thermostat calling for heat?  
White Rodgers Gas Valve  
An inlet post located on the gas valve provides access to  
the supply pressure. See figure 35. Back out the 3/32 hex  
screw one turn, connect a piece of 5/16 tubing and connect  
to a manometer to measure supply pressure. See table 22  
for supply line pressure.  
2 − Are access panels securely in place?  
3 − Is the main disconnect switch closed?  
4 − Is there a blown fuse or tripped circuit breaker?  
5 − Is the filter dirty or plugged? Dirty or plugged filters will  
cause the limit control to shut the unit off.  
6 − Is gas turned on at the meter?  
Honeywell Gas Valve  
A threaded plug on the inlet side of the gas valve provides  
access to the supply pressure tap. Remove the threaded  
plug, install a field−provided barbed fitting and connect a  
manometer to measure supply pressure. See table 22 for  
supply line pressure. Replace the threaded plug after mea-  
surements have been taken.  
7 − Is the manual main shut-off valve open?  
8 − Is the internal manual shut-off valve open?  
9 − Is the unit ignition system in lock out? If the unit locks out  
again, call the service technician to inspect the unit for  
blockages.  
10 −Is pressure switch closed? Obstructed flue will cause  
unit to shut off at pressure switch. Check flue and outlet  
for blockages.  
Manifold Pressure  
NOTE − Pressure test adapter kit (10L34) is available from  
Lennox to facilitate manifold pressure measurement.  
11 −Are flame rollout switches tripped? If flame rollout  
switches are tripped, call the service technician for in-  
spection.  
1 − Connect test gauge to manifold pressure post (figure  
35) or tap (figure 36) on gas valve.  
2 − Ignite unit on high fire and let run for 5 minutes to allow  
for steady state conditions.  
Gas Pressure Adjustment  
3 − After allowing unit to stabilize for 5 minutes, record  
manifold pressure and compare to value given in table  
22.  
Furnace should operate at least 5 minutes before check-  
ing gas flow. Determine time in seconds for two revolu-  
tions of gas through the meter. (Two revolutions assures a  
more accurate time.) Divide by two and compare to time  
in table 20 below. If manifold pressure matches table 22  
and rate is incorrect, check gas orifices for proper size and  
restriction. Remove temporary gas meter if installed.  
4 − If necessary, make adjustments. Figures 35 and 36  
show location of high fire adjustment screw.  
5 − If an adjustment is made on high fire, re−check man-  
ifold pressure on low fire. Do not adjust low fire man-  
ifold pressure. If low fire manifold pressure is more  
than 1/2" above or below value specified in table 22,  
replace valve.  
NOTE − Shut unit off and remove manometer as soon as an  
accurate reading has been obtained. Take care to replace  
pressure tap plug.  
Proper Combustion  
Furnace should operate minimum 15 minutes with correct  
manifold pressure and gas flow rate before checking com-  
bustion. Table 21 shows acceptable combustion for ALL  
SL280UHV models. The maximum carbon monoxide read-  
ing should not exceed 50 ppm.  
TABLE 21  
Firing Rate  
High Fire  
Low Fire  
CO %  
2
CO %  
For L.P.  
For Nat  
2
6.8 − 7.4  
4.2 − 5.7  
7.5 − 9.0  
5.0 − 6.0  
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High Altitude  
IMPORTANT  
For safety, shut unit off and remove manometer as  
soon as an accurate reading has been obtained.  
Take care to replace pressure tap plug.  
The manifold pressure, gas orifice and pressure switch  
may require adjustment or replacement to ensure proper  
operation at higher altitudes. Tables 22 through 25 shows  
manifold pressure, pressures switch and gas conversion  
kits at all altitudes.  
TABLE 22  
Manifold Pressure Settings  
Manifold  
Pressure in.wg.  
0−4500 ft.  
Manifold  
Pressure in.wg.  
4501−7500 ft.  
Manifold  
Pressure in.wg.  
7501 − 10,000 ft.  
Supply Line  
Pressure  
in. w.g.  
Orifice Size  
7501 −  
10,000 ft.  
2
Unit  
Input  
Orifice Size  
0 − 7500 ft.  
Gas  
1
Low  
Fire  
High  
Fire  
Low  
Fire  
High  
Fire  
Low  
Fire  
High  
Fire  
Min  
Max  
Natural  
LP/propane3  
Natural  
.063  
.039  
.063  
.039  
.063  
.039  
.063  
.039  
.055  
.037  
.055  
.037  
.055  
.037  
.055  
.037  
1.7  
4.9  
1.7  
4.9  
1.7  
4.9  
1.7  
4.9  
3.5  
10.0  
3.5  
1.6  
4.9  
1.5  
4.9  
1.5  
4.9  
1.6  
4.9  
3.4  
10.0  
3.2  
1.7  
4.9  
1.7  
4.9  
1.7  
4.9  
1.7  
4.9  
3.5  
10.0  
3.5  
4.5  
11.0  
4.5  
13.0  
13.0  
13.0  
13.0  
13.0  
13.0  
13.0  
13.0  
070  
090  
110  
135  
LP/propane3  
Natural  
10.0  
3.5  
10.0  
3.2  
10.0  
3.5  
11.0  
4.5  
LP/propane3  
Natural  
10.0  
3.5  
10.0  
2.8  
10.0  
3.5  
11.0  
4.5  
LP/propane3  
10.0  
10.0  
10.0  
11.0  
1
2
3
This is the only permissible derate for these units.  
Natural gas high altitude orifice kit required.  
A natural to L.P. propane gas changeover kit is necessary to convert this unit. Refer to the changeover kit installation instruction for the conversion  
procedure.  
NOTE − Units may be installed at altitudes up to 4500 ft. above sea level without modifications.  
TABLE 23  
High Altitude Pressure Switch Kits  
High Altitude  
Unit  
Input  
Pressure Switch Kit  
0 − 4500 ft.  
No Change  
No Change  
No Change  
No Change  
4501 − 7500 ft.  
No Change  
69W56  
7501 − 10,000 ft.  
070  
090  
110  
135  
73W35  
73W35  
73W35  
73W34  
69W56  
73W33  
TABLE 24  
Honeywell Gas Valve Conversion Kits  
TABLE 25  
White Rodgers Gas Valve Conversion Kits  
LP/Propane  
LP/Propane  
High Altitude  
Natural Gas  
Orifice Kit  
High Altitude  
Natural Gas  
Orifice Kit  
Natural Gas to  
LP/ Propane Kit  
Natural Gas to  
LP/ Propane Kit  
to  
Natural Gas  
Kit  
to  
Natural Gas  
Kit  
Unit  
Input  
Unit  
Input  
7501 −  
10,000 ft.  
7501 −  
7501 −  
10,000 ft.  
7501 −  
0 − 7500 ft.  
0 − 7500 ft.  
0 − 7500 ft.  
0 − 7500 ft.  
10,000 ft.  
73W38  
73W38  
73W38  
73W38  
10,000 ft.  
77W11  
77W11  
77W11  
77W11  
070  
090  
110  
135  
73W37  
73W37  
73W37  
73W37  
51W02  
51W02  
51W02  
51W02  
69W79  
69W79  
69W79  
69W79  
070  
090  
110  
135  
77W05  
77W05  
77W05  
77W05  
77W07  
77W07  
77W07  
77W07  
77W09  
77W09  
77W09  
77W09  
Page 53  
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Applications Using a Two−Stage Thermostat  
See figure 37 for ignition control sequence  
A − Heating Sequence −− Integrated Control Thermostat  
Selection DIP Switch 1 OFF in ꢀTwo−Stage" Position  
(Factory Setting)  
Other Unit Adjustments  
Primary and Secondary Limits  
1 − On a call for heat, thermostat first−stage contacts close  
sending a signal to the integrated control. The inte-  
grated control runs a self-diagnostic program and  
checks high temperature limit switches for normally  
closed contacts and pressure switches for normally  
open contacts. The combustion air inducer is ener-  
gized at low speed.  
The primary limit is located on the heating compartment  
vestibule panel. The secondary limits (if equipped) are lo-  
cated in the blower compartment, attached to the back side  
of the blower. These auto reset limits are factory set and re-  
quire no adjustment.  
Flame Rollout Switches (Two)  
2 − Once the control receives a signal that the low pres-  
sure switch has closed, the combustion air inducer be-  
gins a 15−second pre−purge in low speed.  
These manually reset switches are located on (or inside of)  
the burner box. If tripped, check for adequate combustion  
air before resetting.  
NOTE − If the low fire pressure switch does not close  
the combustion air inducer will switch to high fire. After  
a 15 second pre−purge the high fire pressure switch  
will close and the unit will begin operation on high fire.  
After 10 to 20 seconds of high fire operation the unit  
will switch to low fire..  
Pressure Switches  
The pressure switch assembly (includes two switches) is  
located in the heating compartment adjacent to the com-  
bustion air inducer. These switches check for proper com-  
bustion air inducer operation before allowing ignition trial.  
The switches are factory−set and require no adjustment.  
3 − After the pre−purge is complete, a 20−second initial ig-  
nitor warm−up period begins. The combustion air in-  
ducer continues to operate at low speed.  
4 − After the 20−second warm−up period has ended, the gas  
valve is energized on low fire (first stage) and ignition oc-  
curs. At the same time, the control module sends a sig-  
nal to begin an indoor blower 30−second ON−delay.  
When the delay ends, the indoor blower motor is ener-  
gized on the low fire heating speed, the HUM contacts  
close energizing the humidifier and 120V ACC termi-  
nal is energized. The furnace will continue this opera-  
tion as long as the thermostat has a first−stage heating  
demand.  
Temperature Rise  
Place the unit into operation with a second−stage heating  
demand. After supply and return air temperatures have  
stabilized, check the temperature rise. If necessary, adjust  
the heating blower speed to maintain the temperature rise  
within the range shown on the unit nameplate. Increase the  
blower speed to decrease the temperature rise. Decrease  
the blower speed to increase the temperature rise. Failure  
to properly adjust the temperature rise may cause erratic  
limit operation.  
5 − If second−stage heat is required, the thermostat sec-  
ond−stage heat contacts close and send a signal to the  
integrated control. The integrated control initiates a  
30−second second−stage recognition delay.  
Thermostat Heat Anticipation  
6 − At the end of the recognition delay, the integrated con-  
trol energizes the combustion air inducer at high  
speed. The control also checks the high fire (second  
stage) pressure switch to make sure it is closed. The  
high fire (second stage) gas valve is energized and the  
indoor blower motor is energized for operation at the  
high fire heating speed.  
Set the heat anticipator setting (if adjustable) according to  
the amp draw listed on the wiring diagram that is attached  
to the unit.  
NOTE − Do not secure the electrical conduit directly to the  
air ducts or structure.  
7 − When the demand for high fire (second stage) heat is  
satisfied, the combustion air inducer is switched to the  
low−fire heating speed and the high−fire (second  
stage) gas valve is de−energized. The low−fire (first  
stage) gas valve continues operation. The indoor  
blower motor is switched to the low−fire heating speed.  
8 − When the thermostat demand for low−fire (first stage)  
heat is satisfied, the gas valve is de−energized and the  
field−selected indoor blower off delay begins. The  
combustion air inducer begins a 5−second post−purge  
period.  
Heating Sequence of Operation  
Electronic Ignition  
The two−stage, variable speed integrated control used in  
SL280UHV units has an added feature of an internal Watch-  
guard control. The feature serves as an automatic reset de-  
vice for ignition control lockout caused by ignition failure. Af-  
ter one hour of continuous thermostat demand for heat, the  
Watchguard will break and remake thermostat demand to  
the furnace and automatically reset the control to begin the  
ignition sequence.  
9 − When the combustion air post−purge period is com-  
plete, the inducer, the HUM contacts as well as the  
120V ACC terminals are de−energized. The indoor  
blower is de−energized at the end of the off delay.  
NOTE − The ignition control thermostat selection DIP switch is  
factory−set in the ꢀTWO−STAGE" position.  
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Applications Using A Single−Stage Thermostat  
See figure 38 for ignition control sequence  
4 − After the 20−second warm−up period has ended, the gas  
valve is energized on low fire (first stage) and ignition oc-  
curs. At the same time, the control module sends a sig-  
nal to begin an indoor blower 30−second ON−delay.  
When the delay ends, the indoor blower motor is ener-  
gized on the low fire heating speed and the HUM con-  
tacts are energized. The integrated control also initi-  
ates a second−stage on delay (factory−set at 7  
minutes; adjustable to 12 minutes).  
B − Heating Sequence −− Integrated Control Thermostat  
Selection DIP Switch 1 ON in ꢀSingle−Stage" Position  
NOTE − In these applications, two−stage heat will be initi-  
ated by the integrated control if heating demand has not  
been satisfied after the field adjustable period (7 or 12 min-  
utes).  
1 − On a call for heat, thermostat first−stage contacts close  
sending a signal to the integrated control. The inte-  
grated control runs a self-diagnostic program and  
checks high temperature limit switches for normally  
closed contacts and pressure switches for normally  
open contacts. The combustion air inducer is ener-  
gized at low speed.  
2 − Once the control receives a signal that the low pres-  
sure switch has closed, the combustion air inducer be-  
gins a 15−second pre−purge in low speed.  
5 − If the heating demand continues beyond the second−  
stage on delay, the integrated control energizes the  
combustion air inducer at high speed. The control also  
checks the high fire (second stage) pressure switch to  
make sure it is closed. The high fire (second stage)  
gas valve is energized and the indoor blower motor is  
energized for operation at the high fire heating speed.  
6 − When the thermostat heating demand is satisfied, the  
combustion air inducer begins a 5−second low speed  
post−purge. The field−selected indoor blower off delay  
begins. The indoor blower operates at the low−fire  
heating speed.  
NOTE − If the low fire pressure switch does not close  
the combustion air inducer will switch to high fire. After  
a 15 second pre−purge the high fire pressure switch  
will close and the unit will begin operation on high fire.  
After 10 to 20 seconds of high fire operation the unit  
will switch to low fire.  
7 − When the combustion air post−purge period is com-  
plete, the inducer, the HUM contacts as well as the  
120V ACC terminals are de−energized. The indoor  
blower is de−energized at the end of the off delay.  
3 − After the pre−purge is complete, a 20−second initial ig-  
nitor warm−up period begins. The combustion air in-  
ducer continues to operate at low speed.  
HEATING OPERATION WITH TWO−STAGE THERMOSTAT  
80  
1
15  
35  
39  
5 SEC  
30* second  
blower  
ꢀon" delay  
blower  
ꢀoff"  
delay  
ON  
OFF  
Trial For  
Ignition  
Post  
Purge  
Pre−Purge  
Ignitor Warm−up  
1 stg heat demand  
low speed CAI  
ignitor  
low fire gas valve  
indoor blower low heat  
30 seconds  
RECOGNITION PERIOD  
2 stg heat demand  
high speed CAI  
high fire gas valve  
indoor blower high heat  
®
* Conventional thermostat 30 seconds, icomfort Touch thermostat set for 30 adjustable 15 to 45 seconds.  
FIGURE 37  
HEATING OPERATION WITH SINGLE STAGE THERMOSTAT  
15  
35  
39  
5 SEC  
1
80  
blower  
ꢀoff"  
delay  
30* second  
blower  
ꢀon" delay  
Trial For  
Ignition  
ON  
Ignitor Warm−up  
Pre−Purge  
Post  
Purge  
OFF  
heat demand  
low speed CAI  
ignitor  
low fire gas valve  
indoor blower low heat  
7 or 12 minutes after heating demand begins, furnace switches to high fire (depends on setting)  
high speed CAI  
high fire gas valve  
indoor blower high heat  
®
* Conventional thermostat 30 seconds, icomfort Touch thermostat set for 30 adjustable 15 to 45 seconds.  
FIGURE 38  
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Flue And Chimney  
Service  
1 − Check flue pipe, chimney and all connections for tight-  
ness and to make sure there is no blockage.  
2 − Check unit for proper draft.  
WARNING  
ELECTRICAL SHOCK, FIRE,  
OR EXPLOSION HAZARD.  
Electrical  
1 − Check all wiring for loose connections.  
2 − Check for the correct voltage at the furnace (furnace  
operating). Correct voltage is 120VAC + 10%.  
Failure to follow safety warnings exactly could result  
in dangerous operation, serious injury, death or  
property damage.  
Improper servicing could result in dangerous opera-  
tion, serious injury, death, or property damage.  
Before servicing, disconnect all electrical power to  
furnace.  
When servicing controls, label all wires prior to dis-  
connecting. Take care to reconnect wires correctly.  
Verify proper operation after servicing.  
3 − Check amp−draw on the blower motor with inner blow-  
er panel in place.  
Unit Nameplate__________Actual__________  
Cleaning the Heat Exchanger and Burners  
NOTE − Use papers or protective covering in front of the fur-  
nace during cleaning.  
1 − Turn off both electrical and gas power supplies to fur-  
nace.  
2 − Remove flue pipe and top cap (some applications top  
cap can remain) from the unit.  
At the beginning of each heating season, a qualified techni-  
cian should check the system as follows:  
3 − Label the wires from gas valve, rollout switches, prima-  
ry limit switch and make−up box then disconnect them.  
4 − Remove the screws that secure the combustion air in-  
ducer/pressure switch assembly to the collector box.  
Carefully remove the combustion air inducer to avoid  
damaging blower gasket. If gasket is damaged, it must  
be replaced to prevent leakage.  
Blower  
Check the blower wheel for debris and clean if necessary.  
The blower motors are prelubricated for extended bearing  
life. No further lubrication is needed.  
5 − Remove the collector box located behind the combus-  
tion air inducer. Be careful with the collector box gas-  
ket. If the gasket is damaged, it must be replaced to  
prevent leakage.  
WARNING  
The blower access panel must be securely in place  
when the blower and burners are operating. Gas  
fumes, which could contain carbon monoxide, can  
be drawn into living space resulting in personal inju-  
ry or death.  
6 − Disconnect gas supply piping. Remove the screw se-  
curing the burner box cover and remove cover. Re-  
move the four screws securing the burner manifold as-  
sembly to the vestibule panel and remove the  
assembly from the unit.  
Filters  
All SL280UHV filters are installed external to the unit. Fil-  
ters should be inspected monthly. Clean or replace the fil-  
ters when necessary to ensure that the furnace operates  
properly. Replacement filters must be rated for high veloc-  
ity airflow. Table 1 lists recommended filter sizes.  
7 − Remove screws securing burner box and remove  
burner box.  
8 − NOX units only − Remove screw securing NOX insert.  
Remove NOX insert. See figure 40.  
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SL280UHV BURNER, COMBUSTION AIR INDUCER ASSEMBLY &  
HEAT EXCHANGER REMOVAL  
gasket  
pressure switch  
rollout switch  
flue transition  
ignitor  
heat exchanger  
collector box  
orifice plate  
burner box assembly  
sensor  
gasket  
combustion air inducer  
burners  
manifold and gas valve  
burner box cover plate  
retention rings  
cross over  
FIGURE 39  
9 − Remove screws from both sides, top and bottom of  
vestibule panel.  
13− To clean the combustion air inducer visually inspect and  
using a wire brush clean where necessary. Use com-  
pressed air to clean off debris and any rust.  
10− Remove heat exchanger. It may be necessary to  
spread cabinet side to allow more room. If so, remove  
five screws from the left side or right side of cabinet.  
See figure 41.  
14− Reinstall heat exchanger in vestibule. (Replace the  
five screws in the cabinet from step 10 if removed).  
15− NOX units only − replace NOX inserst.  
11− Back wash using steam. Begin from the burner opening  
on each clam. Steam must not exceed 275°F.  
16− Reinstall collector box and combustion air assembly.  
Reinstall all screws to the collector box and combustion  
air inducer. Failure to replace all screws may cause  
leaks. Inspect gaskets for any damage and replace if  
necessary.  
12− To clean burners, run a vacuum cleaner with a soft brush  
attachment over the face of burners. Visually inspect in-  
side the burners and crossovers for any blockage  
caused by foreign matter. Remove any blockage. Figure  
39 shows burner detail.  
17− Reinstall burner box, manifold assembly and burner box  
cover.  
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SL280UHV NOX INSERTS  
18− Reconnect all wires.  
19− Reconnect top cap and vent pipe to combustion air in-  
ducer outlet.  
20− Reconnect gas supply piping.  
21− Turn on power and gas supply to unit.  
22− Set thermostat and check for proper operation.  
23− Check all piping connections, factory and field, for gas  
leaks. Use a leak detecting solution or other preferred  
means.  
CAUTION  
Some soaps used for leak detection are corrosive to  
certain metals. Carefully rinse piping thoroughly af-  
ter leak test has been completed. Do not use  
matches, candles, flame or other sources of ignition  
to check for gas leaks.  
24− If a leak is detected, shut gas and electricity off and  
repair leak.  
25− Repeat steps 24 and 26 until no leaks are detected.  
26− Replace access panel.  
FIGURE 40  
Remove 5 screws if necessary  
(either side of cabinet)  
1
2
3
4
5
FIGURE 41  
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Planned Service  
The following items should be checked during an annual inspection. Power to the unit must be shut off for the service techni-  
cian’s safety.  
Fresh air grilles and louvers (on the unit and in the room  
where the furnace is installed) − Must be open and unob-  
structed to provide combustion air.  
Operating performance − Unit must be observed during  
operation to monitor proper performance of the unit and the  
vent system.  
Combustion gases − Flue products must be analyzed and  
Burners − Must be inspected for rust, dirt, or signs of water.  
compared to the unit specifications.  
Vent pipe − Must be inspected for signs of water, damaged  
Problems detected during the inspection may make it nec-  
essary to temporarily shut down the furnace until the items  
can be repaired or replaced.  
or sagging pipe, or disconnected joints.  
Unit appearance − Must be inspected for rust, dirt, signs  
of water, burnt or damaged wires, or components.  
Instruct the homeowners to pay attention to their  
furnace. Situations can arise between annual furnace in-  
spections that may result in unsafe operation. For instance,  
items innocently stored next to the furnace may obstruct  
the combustion air supply. This could cause incomplete  
combustion and the production of carbon monoxide gas.  
Blower access panel − Must be properly in place and pro-  
vide a seal between the return air and the room where the  
furnace is installed.  
Return air duct − Must be properly attached and provide  
an air seal to the unit.  
Repair Parts List  
The following repair parts are available through independent Lennox dealers. When ordering parts, include the complete  
furnace model number listed on the CSA International nameplate −− Example: SL280UH070V36A. All service must be  
performed by a licensed professional installer (or equivalent), service agency, or gas supplier.  
Cabinet Parts  
Upper access panel  
Heating Parts  
Flame Sensor  
Blower panel  
Top cap  
Heat exchanger assembly  
Gas manifold  
Control Panel Parts  
Transformer  
Two−speed combustion air inducer  
Two−stage gas valve  
Main burner cluster  
Main burner orifices  
Pressure switch  
Two−stage, variable speed integrated control  
Door interlock switch  
Circuit breaker  
Blower Parts  
Ignitor  
Blower wheel  
Primary limit control  
Flame rollout switch  
Blower housing  
Motor  
Secondary limit  
Motor electronics  
Power choke (1 hp only)  
Motor mounting frame  
Motor capacitor  
Blower housing cutoff plate  
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Integrated Control Diagnostic Modes  
Display  
Action (when button released)  
Remain in idle mode  
No change (idle)*  
Solid ꢁE"  
Enter diagnostic recall mode  
Discharge Air Installed  
Solid ꢁD"  
Solid ꢁF"  
Enter flame signal mode  
Solid ꢁP" (variable speed only)  
Program unit capacity/size (Unit Code)**  
* No change implies the display will continue to show whatever is currently being displayed for normal operation (blinking  
decimal, active error code, heat state, etc..)  
** After the ꢁP" is selected (by releasing the push button) the integrated control will start flashing the ꢁP" on display for 90  
seconds. If push button is pressed again and held during that time, the control will start to display characters corresponding  
to different variable speed furnace models for 3 seconds each. While the wanted character−model is displayed push button  
has to be released. Selected option will flash display for 10 seconds and during that time push button has to be pressed  
and held for 5 seconds. Once control accepts new setting it will store data in non−volatile memory and reset itself. If 10 sec-  
onds expires or push button is held less than 5 seconds, control will exit filed test mode and go in idle without programming  
the unit size.  
Integrated Control Diagnostic Codes  
Press the diagnostic push button and hold it to cycle through a menu of options. Every five seconds a new menu item will be  
displayed. Release the button when the desired mode is displayed.  
When a solid "P" is displayed, the furnace capacity / size is programmed.  
When the solid ꢁE" is displayed, the control enters the Diagnostic Recall (Alarm History). Diagnostic Recall mode menu  
options: No change (displaying error history) remains in Diagnostic Recall mode; solid ꢁ = " exits Diagnostic Recall mode;  
and solid ꢁc" clears the error history. Must press button while flashing ꢁc" is displayed to clear error codes.  
When the solid ꢁF" is displayed, the control enters the Flame Signal Mode. The Flame Signal Mode is exited: with power  
cycle/reset, by pressing and holding the push button until 3 horizontal line are displayed ꢁ= ꢁ, after 10 minutes of entering  
flame signal mode.  
Code  
Diagnostic Codes/Status of Equipment  
Action Required to Clear and Recover  
.
Idle mode (Decimal blinks at 1 Hertz −− 0.5 second ON, 0.5 second OFF).  
A
Cubic feet per minute (cfm) setting for indoor blower (1 second ON, 0.5  
second OFF) / cfm setting for current mode displayed.  
C
d
Cooling stage (1 second ON, 0.5 second OFF) / 1 or 2 displayed / Pause  
/ cfm setting displayed / Pause / Repeat codes).  
Dehumidification mode (1 second ON) / 1 second OFF) / cfm setting dis-  
played / Pause / Repeat Codes).  
h
Heat pump stage (1 second ON, 0.5 second OFF) / % of input rate dis-  
played / Pause / cfm setting / Pause / Repeat codes.  
H
Gas Heat Stage (1 second ON, 0.5 second OFF) / 1 or 2 displayed /  
Pause / cfm  
setting displayed / Pause / Repeat codes. Blinking during ignition.  
dF  
U
Defrost mode.  
Discharge Air Temperature  
Page 60  
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Integrated Control Diagnostic Codes (continued)  
Code  
Diagnostic Codes/Status of Equipment  
Action Required to Clear and Recover  
E 105 Device communication problem − No other devices on RS BUS (Commu- Equipment is unable to communicate. Indicates  
nication  
system).  
numerous message errors. In most cases errors are  
related to electrical noise. Make sure high voltage  
power is separated from RSBus. Check for mis−  
wired and/or loose connections between the stat,  
indoor unit and outdoor unit. Check for a high volt-  
age source of noise close to the system. Fault  
clears after communication is restored.  
E 110 Low line voltage.  
Line Voltage Low (Voltage lower than nameplate  
rating). Check power line voltage and correct. Alarm  
clears 5 seconds after fault recovered.  
E 111 Line voltage polarity reversed.  
Reverse line power voltage wiring. System resumes  
normal operation 5 seconds after fault recovered.  
E 112 Ground not detected  
System shuts down. Provide proper earth ground.  
System resumes normal operation 5 seconds after  
fault recovered.  
E 113 High line voltage.  
Line Voltage High (Voltage higher than nameplate  
rating). Provide power voltage within proper range.  
System resumes normal operation 5 seconds after  
fault recovered.  
E 114 Line voltage frequency out−of−range.  
E 115 Low 24V − Control will restart if the error recovers.  
No 60 Hertz Power. Check voltage and line power  
frequency. Correct voltage and frequency problems.  
System resumes normal operation 5 seconds after  
fault recovered.  
24−Volt Power Low (Range is 18 to 30 volts). Check  
and correct voltage. Check for additional power−rob-  
bing equipment connected to system. May require  
installation of larger VA transformer to be installed in  
furnace / air handler. Clears after fault recovered.  
E 116 High 24V.  
24 Volt Power High (Range is 18 to 30 volts). Check  
and correct voltage. Check for proper line voltage  
(120V, 240V, etc.) to equipment. Clears when con-  
trol senses proper voltage.  
E 117 Poor ground detected (Warning only)  
Provide proper grounding for unit. Check for proper  
earth ground to the system. Warning only will clear  
30 seconds after fault recovered.  
E 120 Unresponsive device. Communication only.  
Usually caused by delay in outdoor unit responding  
to indoor unit poling. Recycle power. Check all wir-  
ing connections. Cleared after unresponsive device  
responds to any inquiry.  
E 124 Active communicating thermostat signal missing for more than 3 min-  
utes.  
Equipment lost communication with the thermostat.  
Check four wiring connections, ohm wires and cycle  
power at the thermostat. Alert stops all services and  
waits for heartbeat message from thermostat (sub-  
net controller). Cleared after valid thermostat (sub-  
net controller) message is received.  
E 125 Control failed self−check, internal error, failed hardware. Will restart if  
error  
Hardware problem on the control. Cycle power on  
control. Replace if problem prevents service and is  
recovers. Integrated control not communicating. Covers hardware errors persistent. Critical alert. Cleared 300 seconds after  
(flame sense circuit faults, pin shorts, etc.).  
fault recovered.  
E 126 Control internal communication problem.  
Hardware problem on the control. Cycle power on  
control. Replace if problem prevents service and is  
persistent. Cleared 300 seconds after fault recov-  
ered.  
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Integrated Control Diagnostic Codes (continued)  
E 131 Corrupted control parameters (Verify configuration of system). Communi- Reconfigure the system. Replace control if heating  
cating only.  
or cooling is not available. Only applicable in the  
communicating mode, not in startup. Exit from Com-  
missioning and Execute ’Set Factory Default mode’.  
Control will still operate on default parameter set-  
tings.  
E 180 Outdoor air temperature sensor failure. Only shown if shorted or out−of−  
range.  
Compare outdoor sensor resistance to temperature/  
resistance charts in unit installation instructions.  
Replace sensor pack if necessary. At beginning of  
(any) configuration, furnace or air handler control  
will sense outdoor air and discharge air temperature  
sensor(s). If detected (reading in range), appropri-  
ate feature will be set as ’installed’ and that could  
be seen in ’About’ screen. In normal operation after  
control recognizes sensors, alarm will be sent if  
valid temperature reading is lost. To get rid of set-  
ting and alarm, redo configuration and make sure  
that temperature sensor is marked as ’not installed’  
in Indoor Unit ’About’ screen. When Indoor unit con-  
trol is replaced, thermostat will ’tell’ new control if  
temperature sensor is in system or not. Clears 30  
seconds after fault recovered.  
E 200 Hard lockout − Rollout circuit open or previously open.  
Correct cause of rollout trip, or replace flame rollout  
switch. Test furnace operation. Cleared after fault  
recovered.  
E 201 Indoor blower communication failure − Unable to communicate with blow- Indoor blower communication failure (including pow-  
er motor.  
er outage). Lost communication with indoor blower  
motor. Possible causes: motor not powered, loose  
wiring. Problem may be on control or motor side.  
Cleared after fault recovered.  
E 202 Indoor blower motor mis−match − Indoor motor horsepower does not  
match unit capacity. See Page 67.  
Incorrect appliance capacity code selected. Check  
for proper configuring under: Unit Size Codes for  
Furnace/Air Handler on configuration guide or in  
installation instructions. Cleared after the correct  
match is detected following a reset. (Remove ther-  
mostat from system while applying power and re-  
programming.)  
E 203 Appliance capacity / size is NOT programmed. Invalid unit codes refer to No appliance capacity code selected. Check for  
configuration flow chart. See Page 67.  
proper configuring under: Unit Size Codes for Fur-  
nace on configuration guide or in installation instruc-  
tions. Critical Alert. Cleared after valid unit code is  
read following a reset. (Remove thermostat from  
system while applying power and reprogramming.)  
E 204 Gas valve mis−wired.  
Check gas valve operation and wiring. Clears when  
repaired.  
E 205 Gas valve control relay contact shorted.  
Check wiring on control and gas valve. If wiring is  
correct, replace control.  
st  
E 206 Gas valve second−stage relay failure  
Furnace will operate on 1 stage for remainder of  
the heating demand. Will clear after fault recovered.  
If unable to operate 2nd stage, replace control.  
E 207 Hot surface ignitor sensed open − Refer to troubleshooting. See Page 68. Measure resistance of hot surface ignitor. Replace if  
open or not within specified range found in IOM.  
Resumes normal operation after fault is cleared.  
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Integrated Control Diagnostic Codes (continued)  
Code  
Diagnostic Codes/Status of Equipment  
Low pressure switch failed open.  
Action Required to Clear and Recover  
E 223  
Check pressure (inches w.c.) of low pressure switch  
closing on heat call. Measure operating pressure  
(inches w.c.). Inspect vent and combustion air in-  
ducer for correct operation and restriction. Re-  
sumes normal operation after fault is cleared  
E 224  
Low pressure switch failed closed − Refer to troubleshooting. See  
Page 68.  
Check operation of low pressure switch to see if it is  
stuck closed on heat call longer than 150 seconds.  
Measure operating pressure (inches w.c.). Inspect  
vent and combustion air inducer for correct opera-  
tion and restriction. Resumes normal operation after  
fault is cleared.  
E 225  
E 226  
E 227  
E 228  
High pressure switch failed open − Refer to troubleshooting. See  
Page 68.  
Check pressure (inches w.c.) of high pressure  
switch closing on heat call. Measure operating pres-  
sure (inches w.c.). Inspect vent and combustion air  
inducer for correct operation and restriction. Re-  
sumes normal operation after fault is cleared.  
High pressure switch failed closed − Refer to troubleshooting. See  
Page 68.  
Check operation of high pressure switch closing on  
heat call. Measure operating pressure (inches w.c.).  
Inspect vent and combustion air inducer for correct  
operation and restriction. Resumes normal opera-  
tion after fault is cleared.  
Low pressure switch open during trial for ignition or run mode. Refer to  
troubleshooting. See Page 68.  
Check pressure (inches w.c.) of low pressure switch  
closing on heat call. Measure operating pressure  
(inches w.c.). Inspect vent and combustion air in-  
ducer for correct operation and restriction. Re-  
sumes normal operation after fault is cleared.  
Combustion air inducer calibration failure  
Ignition on high fire  
Unable to perform pressure switch calibration.  
Check vent system and pressure switch wiring con-  
nections. Resumes normal operation after fault is  
cleared.  
E 229  
E 240  
IFC switched to high fire ignition because low fire  
pressure switch did not close in allowed time. No  
action is needed.  
Low flame current − Run mode − Refer to troubleshooting. See Page 68. Check micro−amperes of flame sensor using control  
diagnostics or field−installed mode. Clean or replace  
sensor. Measure voltage of neutral to ground to en-  
sure good unit ground. Alert clears after current  
heat call has been completed.  
E 241  
E 250  
Flame sensed out of sequence − Flame still present.  
Limit switch circuit open − Refer to troubleshooting.  
Shut off gas. Check for gas valve leak. Replace, if  
necessary. Alert clears when fault is recovered.  
Check for proper firing rate on furnace. Ensure  
there is no blockage in heater. Check for proper air  
flow. If limit not closed within 3 minutes, unit will go  
into 1−hour soft lockout. Resumes normal operation  
after fault is cleared.  
E 252  
E 270  
Discharge air temperature too high (gas heat only).  
Check temperature rise, air flow and input rate.  
Cleared when heat call is finished.  
Soft lockout − Exceeded maximum number of retries. No flame current  
sensed.  
Check for proper gas flow. Ensure that ignitor is  
lighting burner. Check flame sensor current. Clears  
when heat call finishes successfully.  
E 271  
Soft lockout − Exceeded maximum number of retries. Last retry failed due Check pressure (inches w.c.) of low pressure switch  
to the pressure switch opening.  
closing on heat call. Measure operating pressure  
(inches w.c.). Inspect vent and combustion air in-  
ducer for correct operation and restriction. Clears  
when heat call finishes successfully.  
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Integrated Control Diagnostic Codes (continued)  
E 272  
Soft lockout − Exceeded maximum number of recycles. Last recycle due  
to the pressure switch opening.  
Check operation of low pressure switch to see if it is  
stuck closed on heat call. Check pressure (inches  
w.c.) of high pressure switch closing on heat call.  
Measure operating pressure (inches w.c.). Inspect  
vent and combustion air inducer for correct opera-  
tion and restriction. Clears when heat call finishes  
successfully.  
E 273  
E 274  
Soft lockout − Exceeded maximum number of recycles. Last recycle due  
to flame failure.  
Check micro−amperes of flame sensor using control  
diagnostics or field−installed mode. Clean or replace  
sensor. Measure voltage of neutral to ground to en-  
sure good unit ground. Clears when heat call finish-  
es successfully.  
Soft lockout − Exceeded maximum number of recycles. Last recycle  
failed due to the limit circuit opening or limit remained open longer than  
3 minutes.  
Shut down system. 1−hour soft lockout. Check firing  
rate and air flow. Check for blockage. Clears when  
heat call finishes successfully.  
E 275  
E 276  
Soft lockout − Flame sensed out of sequence. Flame signal is gone.  
Shut off gas. Check for gas valve leak. 1−hour soft  
lockout. Clears when flame has been proven stable.  
Watchguard calibration failure.  
Unable to perform pressure switch calibration.  
Check vent system and pressure switch wiring con-  
nections. 1−hour soft lockout. Clears when calibra-  
tion has finished successfully.  
E 290  
E 291  
E 292  
Ignitor circuit fault − Failed ignitor or triggering circuitry.  
Heat air flow restricted below the minimum.  
Measure resistance of hot surface ignitor. Replace if  
open or not within specifications. 1−hour soft lock-  
out. Clears when flame has been proven stable.  
Check for dirty filter and air flow restriction. Check  
blower performance. 1−hour soft lockout. Cleared  
when heat call finishes successfully.  
Indoor blower motor unable to start due to obstructed wheel, seized  
bearings.  
Indoor blower motor unable to start (seized bear-  
ing, stuck wheel, etc.). Replace motor or wheel if  
assembly does not operate or meet performance  
standards. 1−hour soft lockout. Clears after circula-  
tor successfully starts.  
E 294  
Combustion air inducer over current.  
Check combustion blower bearings, wiring and  
amps. Replace if does not operate or does not meet  
performance standards. Clears after inducer current  
is sensed to be in−range after the ignition following  
the soft lockout or reset.  
E 295  
E 310  
Indoor blower motor temperature is too high.  
Indoor blower motor over temperature (motor  
tripped on internal protector). Check motor bearings  
and amps. Replace if necessary. Cleared after  
blower demand is satisfied.  
Discharge error temperature sensor failure. Only shown if shorted or  
out of range.  
Compare outdoor sensor resistance to temperature/  
resistance charts in installation instructions. Re-  
place sensor if necessary. Cleared in Communicat-  
ing mode: 30 seconds after fault recovered. In Non−  
Communicating mode: Cleared after the current  
heat call is completed.  
E 311  
Heat rate reduced to match indoor blower air flow.  
Warning Only. Furnace blower in cutback mode due  
to restricted airflow. Reduce firing rate every 60  
seconds to match available CFM. Check filter and  
duct system. To clear, replace filter if needed or re-  
pair/add duct. 2−stage controls will reduce firing rate  
st  
to 1 stage. Clears when heat call finishes success-  
fully.  
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Integrated Control Diagnostic Codes (continued)  
Code  
Diagnostic Codes/Status of Equipment  
Action Required to Clear and Recover  
E 312  
Restricted air flow in cooling or continuous fan mode is lower than cfm  
setting.  
Warning Only. Restricted airflow − Indoor blower is  
running at a reduced CFM (Cutback Mode − The  
variable speed motor has pre−set speed and torque  
limiters to protect the motor from damage caused  
by operating outside of design parameters (0 to 0.8"  
W.C.. total external static pressure). Check filter and  
duct system. To clear, replace filter if needed or re-  
pair/add duct. Cleared after the current service de-  
mand is satisfied.  
E 313  
Indoor or outdoor unit capacity mismatch. Communication only.  
Incorrect indoor/outdoor capacity code selected.  
Check for proper configuring in installation instruc-  
tions. Alarm is just a warning. The system will oper-  
ate, but might not meet efficiency and capacity pa-  
rameters. Alarm will clear when commissioning is  
exited. Cleared after commissioning is complete.  
E 331  
E 334  
E 347  
Global network connection − Communication link problem.  
Relay ꢁY1" stuck on interated control.  
For Future Use.  
Replace integrated control.  
No 24 Volt output on Y1 of "integrated control" with non communicating  
outdoor unit.  
Operation stopped. Y1 relay / Stage 1 failed. (Pilot  
relay contacts did not close or the relay coil did not  
energize; no input back to IFC chip). Critical Alert.  
Cleared after reset and Y1 input sensed.  
E 348  
No 24 Volt output on Y2 of "integrated control" with non?communicating  
outdoor unit.  
Y2 relay / Stage 2 failed. (Pilot relay contacts did  
not close or the relay coil did not energize; no input  
back to IFC chip). Critical Alert. Cleared after reset  
and Y1 input sensed.  
E 349  
E 370  
No 24 Volts between R & O on "integrated control" with non communi-  
cating outdoor unit (Dual fuel module required for heat pump application). place link or hard−wire. Applicable in non communi-  
cating mode. Critical Alert.  
Configuration link R to O needs to be restored. Re-  
Interlock switch sensed open for 2 minutes.  
LSOM − Compressor internal overload tripped.  
LSOM Compressor long run cycle or low system pressure.  
LSOM − Outdoor unit system pressure trip.  
Control sees the loss of 24VAC for 2 minutes .Ter-  
minate all services and wait for interlock switch to  
close. The alarm will clear when 24VAC is continu-  
ously sensed on DS terminal for a minimum of 10  
seconds or on a power reset.  
E 400  
E 401  
Thermostat demand Y1 is present; but, compressor  
is not running. Check power to outdoor unit. Clears  
the error after current is sensed in both RUN and  
START sensors for at least 2 seconds, or after ser-  
vice is removed, or after power reset.  
Compressor ran more than 18 hours to satisfy a  
single thermostat demand. Critical Alert. Clears the  
error after 30 consecutive normal run cycles or  
power reset. Also monitors low pressure switch  
trips.  
E 402  
E 403  
E 404  
Discharge or suction pressure out−of−limits, or com-  
pressor overloaded. Clears the error after 4 consec-  
utive normal compressor run cycles.  
LSOM − Compressor short−cycling. .(Running less than 4 minutes). Out-  
door unit pressure trip  
Compressor runs less than 3 minutes to satisfy a  
thermostat demand. Clears the error after 4 consec-  
utive normal run cycles or power reset.  
LSOM − Compressor rotor locked. Compressor short−cycling. (Running  
less than 4 minutes).  
Compressor rotor locked up due to run capacitor  
short, bearings are seized, excessive liquid refriger-  
ant, etc. Clears the error after 4 consecutive normal  
run cycles or after power reset.  
E 405  
LSOM − Compressor open circuit.  
Compressor circuit open (due to power disconnec-  
tion, open fuse, etc.) Clears the error after 1 normal  
compressor run cycle.  
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Integrated Control Diagnostic Codes (continued)  
E 406  
LSOM − Compressor open start circuit.  
Required amount of current is not passing through  
Start current transformer. Clears the error after cur-  
rent is sensed in START sensor, or after power re-  
set.  
E 407  
LSOM − Compressor open run circuit.  
Required amount of current is not passing through  
Run current transformer. Clears the error after cur-  
rent is sensed in RUN sensor, or 1 normal compres-  
sor run cycle, or after power reset.  
E 408  
E 409  
LSOM − Compressor contactor is welded.  
LSOM − Compressor low voltage.  
Compressor runs continuously. Clears the error  
after 1 normal compressor run cycle or after power  
reset.  
Secondary voltage is below 18VAC. After 10 min-  
utes, operation is discontinued. Clears the code  
after voltage is higher than 20 VAC for 2 seconds or  
after power reset.  
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Program Unit Capacity/Size Mode  
Power−Up − Number displayed represents by integrated control unit size code (furnace model  
and capacity). If three horizontal bars are displayed followed by continuous E203, furnace  
control does not recognize unit size code. Configure per the following:  
−
−
−
Furnace control in IDLE mode  
No heating, cooling or indoor fan  
operation)  
No  
Yes  
To enter Program Unit  
Capacity/Size: push  
and hold button next to  
7−segment LED display  
until solid ꢀP" symbol  
_
Turn room thermostat to OFF  
appears.  
button.  
Release  
IMPORTANT: Field replacement controls may  
need to be manually configured to validate  
furnace unit size code.  
UNIT SIZE  
CODE  
UNIT SIZE  
CODE  
FURNACE MODEL  
FURNACE MODEL  
SL280DF070V36A  
SL280DF090V48B  
SL280DF090V60C  
SL280DF110V60C  
A
b
A
b
SL280UH070V36A  
SL280UH090V36B  
SL280UH090V48B  
SL280UH090V60C  
SL280UH110V60C  
SL280UH135V60D  
C
d
C
d
Solid  
blinking  
7−Segment LED  
P
starts  
on  
P
E
F
When the correct unit size code is displayed, release  
button. Selected code will flash for 10−second period.  
During that period, press and hold push button for 5  
seconds. Integrated control will store code in  
memory and will automatically exit Program Unit  
Capacity/Size Mode and reset. (If second period  
expires or push button is held less than five seconds,  
Push and hold button. Integrated control will  
display unit size code number for each  
furnace model for three seconds.  
control  
will  
automatically  
exit  
Program  
Capacity/Size Mode and go into IDLE mode without  
storing unit size code. If this happens, programming  
function must be repeated).  
−
−
Verify that the selected unit size code is correct  
and stored in non−volatile memory by cycling  
−
the 24 volt power to the furnace control. (At 24  
volt power−up of the furnace control, the  
7−segment LED will display a unit size code. If  
three horizontal bars display, board does not  
recognize unit size code. Programming  
function must be repeated)  
FINISHED  
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Troubleshooting: Heating Sequence of Operation  
CALL FOR FIRST−STAGE HEAT  
1
CALL FOR  
1ST STAGE HEAT  
(LOW FIRE)  
NO  
INDOOR BLOWER OFF AFTER  
HEAT FAN OFF DELAY  
(LOW HEAT SPEED)  
YES  
INDOOR  
BLOWER OFF  
LIMIT  
SWITCH  
HIGH  
LIMIT SWITCH  
CLOSED?  
ERROR  
INDOOR  
BLOWER  
WATCHGUARD −  
AFTER HEAT FAN  
OFF DELAY (LOW  
HEAT SPEED)  
NO  
NO  
CODE  
CLOSED WITHIN 3  
MINUTES?  
ERROR CODE  
FLASHES  
1
FLASHES  
ON(LOW HEAT  
SPEED)  
NO  
YES  
ROLLOUT  
CIRCUIT  
CLOSES  
(MANUAL  
RE−SET)  
INDUCER ON  
(HIGH SPEED)  
ERROR  
CODE  
FLASHES  
ROLLOUT  
CIRCUITS  
CLOSED?  
CALL  
FOR HEAT  
ENDS?  
DE−ENERGIZE  
NO  
NO  
GAS VALVE  
INDOOR BLOWER  
ON (LOW HEAT  
YES  
SPEED)  
YES  
NO  
INDUCER OFF  
AFTER POST  
PURGE  
LOW  
PRESSURE  
SWITCH  
OPEN?  
ERROR CODE  
FLASHES (AFTER  
5 SECONDS)  
INDOOR BLOWER  
OFF AFTER HEAT  
OFF DELAY  
LOW PRESSURE  
SWITCH OPENS  
YES  
YES  
INDUCER ON  
LOW SPEED  
HARD LOCKOUT −  
ERROR CODE  
HIGH  
2
FLASHES  
PRESSURE  
LOW  
SWITCH  
OPEN  
BEFORE  
INDUCER WAS  
TURNED ON?  
PRESSURE SWITCH  
CLOSED WITHIN 120  
SECONDS?  
NO  
LOW & HIGH  
INDUCER TO  
HIGH SPEED−  
ERROR CODE  
FLASHES  
PRESSURE SWITCH  
CLOSED WITHIN 30  
SECONDS?  
NO  
YES  
INDOOR  
BLOWER  
ON?  
YES  
YES  
YES  
NO  
YES  
PRE−PURGE  
(15 SECONDS)  
INDUCER OFF−  
WAIT  
NO  
INDOOR  
BLOWER  
OFF AFTER  
HEAT FAN  
OFF DELAY  
INTERPURGE  
(15 SECONDS)  
5 MINUTES  
ERROR CODE  
FLASHES  
H.S.I. ON  
(20 SECONDS)  
1ST STAGE GAS  
VALVE ENERGIZED  
3
1
NO  
IGNITION TRIAL  
BEGINS (H.S.I. ON)  
HEAT FAN ON DELAY  
TIMER STARTED  
GAS VALVE  
FLAME  
DE−ENERGIZED  
5TH  
WATCHGUARD −  
POSTPURGE  
(5 SECONDS)  
INDUCER  
OFF  
SENSED WITHIN  
4 SECONDS?  
NO  
UNSUCCESSFUL YES  
TRIAL?  
ERROR CODE  
FLASHES  
1
H.S.I. OFF  
YES  
H.S.I. OFF  
1
WATCHGUARD LOCKOUT AUTOMATICALLY RESETS AFTER ONE HOUR  
INDOOR  
HARD LOCKOUT REQUIRES THERMOSTAT RESET OR CYCLING OF POWER TO RESET THE LOCKOUT.  
2
3
BLOWER ON 30 SEC.  
(LOW HEAT SPEED)  
IN CASE HIGH SPEED INDUCER IS RUNNING AT THE TIME THE GAS VALVE GETS ENERGIZED,  
2ND STAGE GAS VALVE IS ENERGIZED INSTEAD OF 1ST STAGE. 20 SECONDS AFTER FLAME  
IS SENSED, INDUCER SWITCHES TO LOW SPEED, AND GAS VALVE SWITCHES TO 1ST STAGE.  
2
CALL FOR HEAT SATISFIED  
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Troubleshooting: Heating Sequence of Operation (Continued)  
CALL FOR SECOND−STAGE HEAT  
2
CALL FOR 2ND STAGE HEAT  
1
(HIGH FIRE)  
SINGLE STAGE  
THERMOSTAT  
2 STAGE THERMOSTAT  
2
2ND STAGE  
ON DELAY  
EXPIRED?  
RECOGNITION DELAY  
(30 SECONDS)  
EXPIRED?  
ONLY FOR 1ST  
REQUEST FOR  
2ND STAGE HEAT  
YES  
YES  
INDUCER SWITCHED  
TO HIGH SPEED  
HIGH  
PRESSURE SWITCH  
CLOSED WITHIN 10  
SECONDS?  
INDUCER SWITCHED  
TO LOW SPEED  
5 MINUTE DELAY  
(ERROR CODE FLASHES)  
NO  
3
YES  
2ND STAGE GAS VALVE  
ENERGIZED  
INDOOR BLOWER ENERGIZED  
ON HIGH HEAT SPEED  
3
CALL FOR HEAT SATISFIED  
1
2
SYSTEM WILL ALWAYS LIGHT ON LOW FIIRE, EVEN IF 2ND STAGE HEAT IS IN PLACE.  
WHEN USED WITH A SINGLE STAGE THERMOSTAT, SET SW1 TO THE ON POSITION IN DIP SWITCH S4.  
3
IF THE HIGH FIRE PRESSURE SWITCH DOES NOT CLOSE WITHIN 5 ATTEMPTS, THE SYSTEM WILL OPERATE AT  
LOW FIRE FOR THE REMAINDER OF THE CALL FOR HEAT REQUEST.  
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Troubleshooting: Heating Sequence of Operation (Continued)  
CALL FOR HEAT SATISFIED  
FIRST−STAGE HEAT  
SECOND−STAGE HEAT  
2
3
RUN MODE:  
1ST OR 2ND STAGE CALL FOR HEAT.  
ALL INPUTS MONITORED (LIMIT, PRESSURE,  
CALL FOR HEAT/COOL, FLAME LEVEL)  
2ND STAGE HEAT  
NO  
2ND STAGE  
CALL FOR HEAT  
SATISFIED?  
YES  
DE−ENERGIZE 2ND STAGE  
GAS VALVE  
INDUCER SPEED SWITCHED  
TO LOW SPEED  
INDOOR BLOWER SWITCHED  
TO LOW HEAT SPEED  
1ST STAGE HEAT  
NO  
1ST STAGE  
CALL FOR HEAT  
SATISFIED?  
YES  
GAS VALVE  
DE−ENERGIZED  
INDUCER OFF AFTER  
5 SECOND POST PURGE  
INDOOR BLOWER OFF  
AFTER FIELD SELECTABLE  
OFF DELAY  
1
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Troubleshooting: Cooling Sequence of Operation (Continued)  
CALL FOR COOLING  
1
1ST STAGE COOLING  
REQUEST RECEIVED  
1
WAIT FOR COMPRESSOR TIMED  
OFF DELAY TO EXPIRE  
ENERGIZE 1ST STAGE  
COOLING CONTACTOR  
(COMPRESSOR & FAN)  
INDOOR BLOWER 2  
SECOND ON DELAY  
ENERGIZE INDOOR BLOWER  
(LOW COOLING MODE)  
2
MAINTAIN INDOOR  
BLOWER  
(LOW COOLING MODE)  
YES  
YES  
1
1ST STAGE  
COOLING REQUEST  
STILL ACTIVE?  
2ND STAGE  
COOLING  
NO  
REQUEST?  
YES  
YES  
ENERGIZE 2ND STAGE  
COOLING CONTACTOR  
(COMPRESSOR & FAN)  
ENERGIZE INDOOR BLOWER  
(HIGH COOLING MODE)  
2
NO  
2ND STAGE  
COOLING REQUEST  
STILL ACTIVE?  
MAINTAIN INDOOR BLOWER  
(HIGH COOLING MODE)  
YES  
NO  
DE−ENERGIZE 2ND  
STAGE COOLING  
CONTACTOR  
(COMPRESSOR & FAN)  
1ST STAGE  
COOLING REQUEST  
STILL ACTIVE?  
ENERGIZE AND MAINTAIN  
INDOOR BLOWER AT  
(LOW COOLING MODE)  
YES  
NO  
DE−ENERGIZE 1ST  
STAGE COOLING  
CONTACTOR  
1
2
CONTROL WILL NOT RESPOND TO A 2ND STAGE COOLING REQUEST UNLESS A 1ST STAGE  
COOLING REQUEST IS ACTIVE.  
(COMPRESSOR & FAN)  
INDOOR BLOWER LOW COOLING MODE AND HIGH COOLING MODE HAVE SPECIFIC ON, OFF  
AND SPEED RAMPING PROFILES. THE SPECIFIC PROFILE IS SELECTED USING THE  
DIP SWITCHES ON THE CONROL.  
DE−ENERGIZE INDOOR  
2
BLOWER  
1
Page 71  
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Troubleshooting: Continuous Fan Sequence of Operation  
CALL FOR FAN  
1
CALL FOR FAN  
INDOOR BLOWER ON  
CONTINUOUS FAN  
SPEED  
NO  
CALL FOR FAN  
REMOVED?  
MAINTAIN INDOOR  
BLOWER AT  
CONTINUOUS FAN  
YES  
REQUEST  
FOR COOLING  
RECEIVED?  
YES  
MAINTAIN INDOOR  
BLOWER AT  
CONTINUOUS FAN  
GO TO CALL FOR COOLING  
4
NO  
REQUEST  
FOR HEAT  
RECEIVED?  
YES  
INDOOR BLOWER OFF  
1
GO TO CALL FOR 1ST STAGE HEAT  
NO  
DE−ENERGIZE INDOOR  
BLOWER  
1
Page 72  
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