INSTALLATION
INSTRUCTIONS
E 2011 Lennox Industries Inc.
Dallas, Texas, USA
ML180UH
®
MERIT SERIES GAS FURNACE
UPFLOW / HORIZONTAL AIR DISCHARGE
506816−01
06/2011
Supersedes 506778−01
Litho U.S.A.
THIS MANUAL MUST BE LEFT WITH THE
HOMEOWNER FOR FUTURE REFERENCE
This is 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.
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.
AIR FLOW
UPFLOW
CAUTION
As with any mechanical equipment, personal injury
can result from contact with sharp sheet metal
edges. Be careful when you handle this equipment.
HORIZONTAL RIGHT
HORIZONTAL LEFT
Table of Contents
Unit Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Parts Arrangement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
ML180UH 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
Gas Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Electrical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Integrated Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Unit Start−Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Gas Pressure Adjustment . . . . . . . . . . . . . . . . . . . . . . . 30
High Altitude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Proper Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Other Unit Adjustments . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Blower Performance Data . . . . . . . . . . . . . . . . . . . . . . . 33
Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Planned Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Repair Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Integrated Control Diagnostic Codes . . . . . . . . . . . . . . 39
Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Setting Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Duct System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Venting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
06/11
506816−01
Page 1
*2P0611*
*P506816-01*
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Parts Arrangement
Make−Up Box
Heat Exchanger
Combustion Air Inducer
Combustion Air Inducer
Pressure Switch
Burner Box
(includes sensor, ignitor
and rollout switches)
Gas Valve
Primary Limit
(under
combustion
air inducer)
Control Box
(includes integrated control,
interlock switch and transformer)
Upper Access Panel
Secondary Limits
Blower Assembly
Blower Access Panel
Capacitor
FIGURE 1
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ML180UH Gas Furnace
CAUTION
The ML180UH unit is shipped ready for installation in the
upflow or horizontal right position (for horizontal left posi-
tion the combustion air pressure switch must be moved).
The furnace is shipped with the bottom panel in place. The
bottom panel must be removed if the unit is to be installed
in a horizontal application. The panel may also be re-
moved 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
ML180UH 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 ML180UH 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
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.
Temperature Rise
NOTE − Furnace must be adjusted to obtain a temperature
rise within the range specified on the unit nameplate. Failure
to do so may cause erratic limit operation and may result in
premature heat exchanger failure.
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.
This ML180UH furnace must be installed so that its electri-
cal components are protected from water.
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Installed in Combination with a Cooling Coil
This furnace design has not been CSA International
certified for installation in mobile homes, recreational
vehicles, or outdoors.
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.
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
Use of Furnace as Construction Heater
Lennox does not recommend the use of ML180UH 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.
ML180UH units may be used for heating of buildings or
structures under construction, if the following conditions
are met:
Heating Unit Installed Parallel to Cooling Coil
D The vent system must be permanently installed per
these installation instructions.
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.
Cooling Coil
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.
Heating Unit Installed Upstream of Cooling Unit
D The input rate and temperature rise must be set per the
furnace rating plate.
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
Cooling Coil
FIGURE 2
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 ML180UH furnace:
The ML180UH furnace may be installed in alcoves, clos-
ets, attics, basements, garages, crawl spaces and utility
rooms in the upflow or horizontal position.
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.
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D Do not install the furnace where drafts might blow direct-
ly into it. This could cause improper combustion and un-
safe operation.
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 block the furnace combustion air openings with
clothing, boxes, doors, etc. Air is needed for proper
combustion and safe unit operation.
D When the furnace is installed in an attic or other insu-
lated space, keep insulation away from the furnace.
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.
NOTE − The Commonwealth of Massachusetts stipu-
lates these additional requirements:
D Gas furnaces shall be installed by a licensed plumb-
er or fitter only.
D The gas cock must be ꢀT handle" type.
D When a furnace is installed in an attic, the passage-
way to and service area surrounding the equipment
shall be floored.
CAUTION
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:
WARNING
Product contains fiberglass wool.
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.)
Permanent wave solutions
Chlorinated waxes and cleaners
Chlorine base swimming pool chemicals
Water softening chemicals
De-icing salts or chemicals
Fiberglass wool may also cause respiratory, skin,
and eye irritation.
Carbon tetrachloride
Halogen type refrigerants
To reduce exposure to this substance or for further
information, consult material safety data sheets
available from address shown below, or contact your
supervisor.
Cleaning solvents (such as perchloroethylene)
Printing inks, paint removers, varnishes, etc.
Hydrochloric acid
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 ML180UH furnaces to ensure efficient
and safe operation. You must consider combustion air
needs and requirements for exhaust vents and gas piping.
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
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-
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 6.
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)
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 3
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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)
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 4
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
WATER
HEATER
NOTE − Each air duct opening shall have a free area of at least one
2
square inch (645 mm ) per 2,000 Btu (.59 kW) per hour of the total
NOTE−The inlet and outlet air openings shall each have a
2
input rating of all equipment in the enclosure. If the equipment room
is located against an outside wall and the air openings communi-
cate directly with the outdoors, each opening 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.
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 5
FIGURE 6
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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-
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 ML180UH 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
NOTE − Units with 1/2 hp blower motors are equipped with
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 C
Type of Vent
Connector
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‡
ML180UH09048B 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.
** 4−1/2 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
in. cabinets, or 2inches if a single wall vent pipe is used on 17−1/2
in. cabinets.
FIGURE 8
FIGURE 7
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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 X 635mm 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 − Single side return air with transition to accommodate 20
x 25 x 1 in. (508 x 635 x 25 mm) cleanable air filter. (Re-
quired to maintain proper air velocity.) See figure 9.
AIR FLOW
2 − Single side return air with optional return airbase. See fig-
Transition
3 − Bottom return air.
4 − Return air from both sides.
5 − Bottom and one side return air.
Refer to Engineering Handbook for additional information.
FIGURE 9
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
QUALITY
CABINET
(PCO, Filter
Cabinet, etc.)
2
1 22−7/16
(570)
Maximum
1 Unit side return air
Opening
14 (356)
Overall
AIR FLOW
MUST
(Maximum)
COVER BOTH
UNIT AND
RETURN
AIR BASE
OPENINGS
SIDE RETURN
5−5/8
(143)
7−1/4
(184)
AIR OPENINGS
(Either Side)
23
OPTIONAL
RETURN
AIR BASE
3/4
(19)
(584)
26−7/8
14−1/2 (368) A Width (65W75)
17−1/2 (446) B Width (50W98)
21 (533) C Width (50W99)
24−1/2 (622) D Width (51W00)
(683)
SIDE VIEW
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 356 mm) is preferred.
FIGURE 10
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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 ML180UH furnace can be installed in horizontal ap-
plications. Order horizontal suspension kit (51W10) from
Lennox, or use equivalent suspension method.
Allow for clearances to combustible materials as indicated
on the unit nameplate. Minimum clearances for closet or al-
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
Typical Horizontal Application
Unit Suspended in Attic or Crawlspace
Metal
Strap
Internal
Brace
3/16
Bracket
Screw
Air Flow
Bottom Cap
Bottom Panel
FIGURE 11
FIGURE 13
Horizontal Application
Installation Clearances
Top
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.
Left
End
Right
End
Bottom
Type C
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.
Vent Connector
Type
Type B1
Return Air −− Horizontal Applications
Top
*Front
Back
Ends
Vent
0
2−1/4 in. (57 mm)**
0
0
2−1/4 in. (57 mm)
0
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
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.
** 4−1/2 in. if singlewall 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 12
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TABLE 1
Horizontal Application
Unit Installed on Platform
Filter Size
Furnace
Cabinet Width
Line contact is permissible but not preferred
See the unit nameplate for
Side Return
Bottom Return
clearances.
A − 14−1/2"
B − 17−1/2"
C − 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)
D − 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 0.5 inches
w.c. Higher external static pressures may cause erratic lim-
it operation.
FIGURE 14
Supply Air Plenum
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.
WARNING
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 a gas 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 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.
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
A filter must be in place any time the unit is operating.
Page 12
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secure the combustion air inducer / pressure switch
assembly to the orifice plate. Lift the assembly and ro-
tate it 90 degrees clockwise or counterclockwise to ei-
ther the 3 o’clock position or to 9 o’clock position. Re−
secure 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 16
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
Flue Transition
Mounting Screws
UPFLOW POSITION
Left Side Vent Discharge
Pressure
Switch
Collector Box
Make−Up
Box
Vent Pipe
FIGURE 15
Flue
Transition
Upflow Position
UPFLOW POSITION
Top Vent Discharge
Vent Pipe
FLOW
AIR
Flue
D Gas supply piping must be brought into the unit from the right
side in order to accommodate the flue pipe.
Transition
Collector Box
Pressure
Switch
D Cut combustion air inducer tubing from 9" to 8" to avoid
interference with inducer motor
D 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.
Make−Up
Box
D Re−secure make−up box wires: Either pull excess wires
through the blower compartment and secure using supplied
wire tie, or coil excess wire and secure to the gas manifold.
FIGURE 17
UPFLOW POSITION
Right Side Vent Discharge
Flue Transition
Vent Pipe
Cover Plate
Collector Box
Pressure
Switch
FLOW
AIR
FIGURE 16
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
D Cut combustion air inducer tubing from 9" to 5" to avoid
interference with inducer motor
If necessary, reposition the combustion air inducer, pres-
sure switch and/or make−up box as needed per the follow-
FIGURE 18
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HORIZONTAL RIGHT POSITION
Top Vent Discharge
HORIZONTAL LEFT POSITION
Top Vent Discharge
Vent Pipe
Vent Pipe
Pressure Switch
Pressure
Switch
Flue
Transition
Cover Plate
AIR
AIR
Flue
Transition
FLOW
FLOW
Collector Box
Make−Up Box
Cover Plate
Collector Box
Make−Up Box
D 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.
D Gas supply piping must be brought into the unit from the bot-
tom in order to accommodate the flue pipe.
D Cut combustion air inducer tubing from 9" to 8" to avoid
interference with inducer motor
D 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.
D Re−secure pressure switch wires: Either pull excess wires
through the blower compartment and secure using supplied
wire tie, or coil excess wire and secure to the gas manifold.
D Re−secure make−up box wires: Either pull excess wires through
the blower compartment and secure using supplied wire tie, or
coil excess wire and secure to the gas manifold.
FIGURE 19
HORIZONTAL LEFT POSITION
Side Vent Discharge
FIGURE 21
Pressure Switch
AIR
HORIZONTAL RIGHT POSITION
Side Vent Discharge
Make−Up Box
FLOW
Pressure Switch
Vent Pipe
AIR
Make−Up Box
Collector Box
D Cut combustion air inducer tubing from 9" to 7" to avoid
interference with inducer motor
FLOW
D 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.
Flue Transition
Collector Box
D Re−secure pressure switch wires: Either pull excess wires
through the blower compartment and secure using supplied
wire tie, or coil excess wire and secure to the gas manifold.
FIGURE 22
FIGURE 20
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The ML180UH 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
ML180UH is not approved for use with horizontal venting.
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
mon venting.
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.
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
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.
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.
Insulation for the flexible vent pipe must be an encapsu-
lated fiberglass sleeve recommended by the flexible vent
Refer to the tables and the venting information contained in
these instructions to properly size and install the venting
system.
IMPORTANT
Once the venting system is installed, attach the ꢀDis-
connected Vent" warning sticker to a visible area of
warning sticker is provided in the bag assembly. Or-
der kit 66W04 for additional stickers.
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
Install the first vent connector elbow at a minimum of six
inches (152 mm) from the furnace vent outlet. See figure
23.
WARNING
Asphyxiation hazard. The exhaust vent for this fur-
nace must be securely connected to the furnace flue
transition at all times.
Venting Using a Masonry Chimney
The following additional requirements apply when a lined
masonry chimney is used to vent this furnace.
VENT CONNECTION UPFLOW AND HORIZONTAL POSITION
“DISCONNECTED VENT”
WARNING
STICKER
VENT PIPE
(min. 6" length)
“DISCONNECTED VENT”
WARNING
STICKER
FLUE TRANSITION
COLLAR
FLUE
TRANSITION
COLLAR
VENT PIPE
(min. 6" length)
FIGURE 23
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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 ML180UH series units. The chimney
passageway must be checked periodically to ensure that it
is clear and free of obstructions.
Common Venting Using Metal−Lined Masonry Chimney
SEALED
MAX. LENGTH
−− SEE NOTE 1
BELOW.
5 ft. (1.5 m)
minimum
MIN. LENGTH −− AS
SHORT AS PRACTICAL
EXTERIOR
CHIMNEY WITH
METAL
Do not install a manual damper, barometric draft regulator,
or flue restrictor between the furnace and the chimney.
LINER
VENT CONNECTOR
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.
4 in. (102 mm)
minimum
FURNACE
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.
OTHER
APPLIANCE
PERMANENTLY
SEALED FIREPLACE
OPENING
General Venting Requirements
Vent all ML180UH furnaces according to these instruc-
tions:
NOTE 1 − Refer to the provided venting tables for installations. Refer
to the capacity requirements shown in the provided venting tables.
1 − Vent diameter recommendations and maximum allow-
able piping runs are found in the provided venting
tables.
FIGURE 24
DO NOT insulate the space between the liner and the
chimney wall with puffed mica or any other loose gran-
ular insulating material.
2 − In no case should the vent or vent connector diameter
be less than the diameter specified in the provided
venting tables.
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.
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.
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 fan−assisted furnace may be commonly vented into an
existing lined masonry chimney if the following conditions
are met:
S The chimney is currently serving at least one drafthood−
equipped appliance;
S The vent connectors and chimney are sized according
to the provided venting tables.
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.
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.
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.
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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
FIGURE 25
6 − The entire length of single wall metal vent connector
shall be readily accessible for inspection, cleaning,
and replacement.
1-1/2 feet (.46 m) for each inch (25 mm) of common
vent diameter.
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.
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).
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
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.
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
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.
Maximum Horizontal
Connector Length feet (m)
Connector Diameter
inches (mm)
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)
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).
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
15 − No portion of the venting system can extend into, or pass
through any circulation air duct or plenum.
Page 17
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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.
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.
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).
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.
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
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
NA
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
NA
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
NA
54
56
73
93
NA
NA
53
55
72
91
115
NA
NA
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
NA
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
NA
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
NA
0
2
39
51
85
6
8
4
NA
NA
37
NA
NA
83
92
102
114
83
6
89
0
164
108
102
95
2
39
56
83
5
NA
NA
37
NA
NA
87
107
122
82
8
0
174
117
111
100
190
136
128
116
NA
2
39
61
82
10
5
52
56
105
132
80
10
0
NA
36
NA
93
2
38
69
80
5
51
63
102
128
158
78
15
10
15
0
NA
NA
35
NA
NA
96
200
148
140
129
NA
2
37
74
78
5
50
68
100
125
155
186
76
20
10
15
20
0
NA
NA
NA
34
NA
NA
NA
99
NA
211
164
157
144
131
NA
2
37
80
76
5
49
74
98
10
15
20
30
NA
NA
NA
NA
NA
NA
NA
NA
122
151
181
NA
30
NA
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
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
49
MAX
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
56
MIN
NA
NA
NA
NA
NA
NA
NA
84
MAX
NA
NA
NA
NA
NA
NA
NA
85
MIN
NA
MAX
NA
MIN
NA
MAX
NA
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
NA
NA
168
175
NA
182
198
NA
6
121
NA
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.
5 − After the burner have operated for 5 minutes, test for
leaks of flue gases at the draft hood relief opening. Use
the flame of a match or candle.
WARNING
CARBON MONOXIDE POISONING HAZARD
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.
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.
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.
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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
Gas supply piping should not allow more than 0.5"W.C. drop
in pressure between gas meter and unit. Supply gas pipe
must not be smaller than unit gas connection.
CAUTION
5 − A 1/8" N.P.T. plugged tap or pressure post is located
on the gas valve to facilitate test gauge connection.
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.
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.
2 − When connecting the gas supply piping, consider fac-
tors such as length of run, number of fittings, and fur-
lists recommended pipe sizes for typical applications.
3 − The gas piping must not run in or through air ducts,
clothes chutes, gas vents or chimneys, dumb waiters,
or elevator shafts.
IMPORTANT
Compounds used on threaded joints of gas piping
must be resistant to the actions of liquified petro-
leum gases.
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.
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)
172
(4.87)
118
(3.34)
95
(2.69)
81
(2.29)
72
(2.03)
65
(1.84)
60
(1.69)
56
(1.58)
52
(1.47)
50
(1.42)
3/4
(19.05)
.824
(20.930)
360
(10.19)
247
(7.00)
199
(5.63)
170
(4.81)
151
(4.28)
137
(3.87)
126
(3.56)
117
(3.31)
110
(3.11)
104
(2.94)
1
(25.4)
1.049
(26.645)
678
(19.19)
466
(13.19)
374
(10.59)
320
(9.06)
284
(8.04)
257
(7.27)
237
(6.71)
220
(6.23)
207
(5.86)
195
(5.52)
1−1/4
(31.75)
1.380
(35.052)
1350
(38.22)
957
(27.09)
768
(22.25)
657
(18.60)
583
(16.50)
528
(14.95)
486
(13.76)
452
(12.79)
424
(12.00)
400
(11.33)
1−1/2
(38.1)
1.610
(40.894)
2090
(59.18)
1430
(40.49)
1150
(32.56)
985
(27.89)
873
(24.72)
791
(22.39)
728
(20.61)
677
(19.17)
635
(17.98)
600
(17.00)
2
(50.8)
2.067
(52.502)
4020
(113.83)
2760
(78.15)
2220
(62.86)
1900
(53.80)
1680
(47.57)
1520
(43.04)
1400
(39.64)
1300
(36.81)
1220
(34.55)
1160
(32.844)
2−1/2
(63.5)
2.469
(67.713)
6400 4400
(181.22) (124.59)
3530
(99.95)
3020
(85.51)
2680
(75.88)
2480
(70.22)
2230
(63.14)
2080
(58.89)
1950
(55.22)
1840
(52.10)
3
(76.2)
3.068
(77.927)
11300 7780
6250
5350
4740
4290
3950
3670
(319.98) (220.30) (176.98) (151.49) (134.22) (121.47) (111.85) (103.92)
3450
(97.69)
3260
(92.31)
3
NOTE − Capacity given in cubic feet (m ) of gas per hour and based on 0.60 specific gravity gas.
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Left Side Piping
(Standard)
MANUAL
MAIN SHUT−OFF
VALVE
AUTOMATIC
GAS VALVE
MANUAL
MAIN SHUT−OFF
VALVE
(With 1/8 in. NPT
Plugged Tap Shown)
(With 1/8 in. NPT
Plugged Tap
Shown)
GROUND
JOINT
UNION
AUTOMATIC
GAS VALVE
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 26
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
GROUND
JOINT
UNION
FIELD
PROVIDED
AND INSTALLED
Horizontal Application
Right−Side Air Discharge
NOTE − BLACK IRON PIPE ONLY TO BE ROUTED INSIDE OF CABINET
DRIP LEG
FIGURE 27
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Leak Check
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.
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.
INTERIOR MAKE−UP BOX INSTALLATION
CAUTION
Right Side
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.
BOX
The furnace must be isolated by closing its individual
manual shut-off valve and disconnecting from from the gas
supply system the during any pressure testing of the gas
supply system at pressures greater than 1/2 psig (3.48
kPa, 14 inches w.c.).
FIGURE 29
IMPORTANT
When testing pressure of gas lines, gas valve must
valves can be damaged if subjected to pressures
greater than 1/2 psig (3.48 kPa, 14 inches w.c.).
INTERIOR MAKE−UP BOX INSTALLATION
Left side
MANUAL MAIN
ISOLATE
SHUT−OFF VALVE
WILL NOT HOLD
NORMAL TEST
PRESSURE
GAS VALVE
BOX
FURNACE
1/8 NPT PLUG
CAP
FIGURE 28
Electrical
ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures
FIGURE 30
CAUTION
The power supply wiring must meet Class I restrictions.
Protected by either a fuse or circuit breaker, select circuit
protection and wire size according to unit nameplate.
Electrostatic discharge can affect electronic com-
ponents. Take precautions during furnace installa-
tion and service to protect the furnace’s electronic
controls. Precautions will help to avoid control ex-
posure to electrostatic discharge by putting the fur-
nace, the control and the technician at the same
electrostatic potential. Neutralize electrostatic
charge by touching hand and all tools on an un-
painted unit surface, such as the gas valve or blower
deck, before performing any service procedure.
NOTE − Unit nameplate states maximum current draw.
Maximum over−current protection allowed is 15 AMP.
Holes are on both sides of the furnace cabinet to facilitate
wiring.
Install a separate (properly sized) disconnect switch near
the furnace so that power can be turned off for servicing.
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Before connecting the thermostat, check to make sure the
wires will be long enough for servicing at a later date. Make
sure that thermostat wire is long enough to facilitate future
removal of blower for service.
S
S
S
The furnace requires 120 volts + 10% (Range: 108
volts to 132 volts).
The furnace operates at 60 Hz + 5% (Range: 57 Hz to
63 Hz).
The furnace integrated control requires both polarity
and proper ground. Both polarity and proper grounding
should be checked before attempting to operate the
furnace on either permanent or temporary power.
Generator should have a wave form distortion of less
than 5% RHD.
Complete the wiring connections to the equipment. Use the
provided unit wiring diagram and the field wiring diagram
able for Class II rating for thermostat connections.
S
Electrically ground the unit according to local codes or, in
the absence of local codes, according to the current Na-
tional Electric Code (ANSI/NFPA No. 70). A green ground
wire is provided in the field make−up box.
Thermostat
Install the room thermostat according to the instructions
designations. If the furnace is being matched with a heat
pump, refer to the FM21 installation instruction or appropri-
ate dual fuel thermostat instructions.
NOTE − The ML180UH furnace contains electronic compo-
nents that are polarity sensitive. Make sure that the furnace
is wired correctly and is properly grounded.
Accessory Terminals
ML180UH and CONDENSING UNIT
THERMOSTAT DESIGNATIONS
(Refer to specific thermostat and outdoor unit.)
One line voltage ꢀEAC" 1/4" spade terminal is provided on
control configuration. This terminal is energized when the
indoor blower is operating. Any accessory rated up to one
amp can be connected to this terminal with the neutral leg
of the circuit being connected to one of the provided neutral
terminals. If an accessory rated at greater than one amp is
connected to this terminal, it is necessary to use an exter-
nal relay.
Thermostat
Furnace
Condensing
Unit
*CONDENSING
UNITꢁ
POWER
R
R
W1
Y
HEAT
W
Y
CONDENSING
UNITꢁ
COOLING
INDOOR BLOWER
G
G
C
CONDENSING
UNITꢁ COMMON
One line voltage ꢀHUM" 1/4" spade terminal is provided on
the furnace integrated control. See figure 34 for integrated
control configuration. This terminal is energized in the
heating mode when the combustion air inducer is operat-
ing. Any humidifier rated up to one amp can be connected
to this terminal with the neutral leg of the circuit being con-
nected to one of the provided neutral terminals. If a humidi-
fier rated at greater than one amp is connected to this termi-
nal, it is necessary to use an external relay relay.
COMMON
C
*NOTE − ꢀR" REQUIRED ON SOME OUTDOOR UNITS
FIGURE 31
Indoor Blower Speeds
1 − When the thermostat is set to ꢀFAN ON," the indoor
blower will run continuously on the heating speed
when there is no cooling or heating demand.
2 − When the ML180UH is running in the heating mode,
the indoor blower will run on the heating speed.
Generator Use − Voltage Requirements
The following requirements must be kept in mind when
specifying a generator for use with this equipment:
3 − When there is a cooling demand, the indoor blower will
run on the cooling speed.
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ML180UH Schematic Wiring Diagram and Sequence of Operation
8
1
4
3
3
6
5
2
7
1 − When there is a call for heat, W1 of the thermostat energizes W of the furnace control with 24VAC.
2 − Integrated control runs a self−check. S10 primary limit, S47 rollout switch and S21 secondary limit contacts are found to be closed. Call for
heat can continue.
3 − Integrated control (A92) energizes combustion air inducer B6. Combustion air inducer runs until S18 combustion air pressure switch closes .
Once S18 closes, a 15−second pre−purge follows.
4 − Integrated control (A92) energizes ignitor. A 20−second warm−up period begins.
5 − Gas valve opens for a 4−second trial for ignition
6 − Flame is sensed, gas valve remains open for the heat call.
7 − After 45−second delay, integrated control (A92) energizes indoor blower B3.
8 − When heat demand is satisfied, W1 of the indoor thermostat de−energizes W of the ignition control which de−energizes the gas valve
Combustion air inducer B6 continues a 5−second post−purge period, and indoor blower B3 completes a selected OFF time delay.
FIGURE 32
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TYPICAL ML180UH FIELD WIRING DIAGRAM
IGNITOR
*NOTE − ꢀR" REQUIRED ON SOME OUTDOOR UNITS
*R
FIGURE 33
INTEGRATED CONTROL
(Automatic Hot Surface Ignition System)
TERMINAL DESIGNATIONS
Humidifier (120VAC)
HUM
LINE
XFMR
EAC
Input (120VAC)
Transformer (120VAC)
Electronic Air Cleaner (120VAC)
Blower − Cooling Speed (120VAC)
Blower − Heating Speed (120VAC)
Dead terminals to park alternate speed taps
Flame sensor
COOL
HEAT
PARK
FLAME
NEUTRALS
Neutral terminals (120VAC)
3 AMP, 32 VAC FUSE
HEAT FAN OFF
DELAY JUMPER
FIGURE 34
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4 − This furnace is equipped with an ignition device which
automatically lights the burners. Do not try to light the
burners by hand.
Unit Start−Up
FOR YOUR SAFETY READ BEFORE LIGHTING
5 − Remove the upper access panel.
6 − Move switch on gas valve to OFF. Do not force. See
WARNING
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.
Do not use this furnace if any part has been under-
water. A flood−damaged furnace is extremely dan-
gerous. Attempts to use the furnace can result in
fire or explosion. Immediately call a qualified ser-
vice technician to inspect the furnace and to replace
all gas controls, control system parts, and electrical
parts that have been wet or to replace the furnace,
if deemed necessary.
MANIFOLD
MANIFOLD
PRESSURE
PRESSURE
ADJUSTMENT
OUTLET
SCREW
PORT
WARNING
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.
INLET
PRESSURE
PORT
GAS VALVE SHOWN IN ON POSITION
FIGURE 35
8 − Move switch on gas valve to ON. Do not force. See fig-
CAUTION
Before attempting to perform any service or mainte-
nance, turn the electrical power to unit OFF at dis-
connect switch.
9 − Replace the upper access panel.
10− Turn on all electrical power to to the unit.
11− Set the thermostat to desired setting.
NOTE − When unit is initially started, steps 1 through 11
may need to be repeated to purge air from gas line.
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.
12− If the appliance will not operate, follow the instructions
ꢀTurning Off Gas to Unit" and call your service techni-
cian or gas supplier.
The gas valve on the ML180UH 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.
Turning Off Gas to Unit
1 − Set the thermostat to the lowest setting.
2 − Turn off all electrical power to the unit if service is to be
performed.
Placing the furnace into operation:
3 − Remove the upper access panel.
4 − Move switch on gas valve to OFF. Do not force.
ML180UH 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.
5 − Replace the upper access panel.
Failure To Operate
If the unit fails to operate, check the following:
1 − Is the thermostat calling for heat?
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?
WARNING
If you do not follow these instructions exactly, a fire
or explosion may result causing property damage,
personal injury or death.
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.
1 − STOP! Read the safety information at the beginning of
this section.
10 − Is pressure switch closed? Obstructed flue will cause
unit to shut off at pressure switch. Check flue and outlet
for blockages.
2 − Set the thermostat to the lowest setting.
3 − Turn off all electrical power to the unit.
Page 29
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11 − Are flame rollout switches tripped? If flame rollout
switches are tripped, call the service technician for in-
spection.
Supply Pressure Measurement
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
proper line pressure. Replace the threaded plug after mea-
surements have been taken.
Heating Sequence Of Operation
1 − When thermostat calls for heat, combustion air blower
starts.
Manifold Pressure Measurement
2 − Combustion air pressure switch proves blower opera-
tion. Switch is factory−set and requires no adjustment.
1 − Remove the threaded plug from the outlet side of the
gas valve and install a field−provided barbed fitting.
Connect to a manometer to measure manifold pres-
sure.
3 − After a 15−second prepurge, the hot surface ignitor en-
ergizes.
4 − After a 20−second ignitor warm−up period, the gas
valve solenoid opens. A 4−second trial for ignition peri-
od begins.
2 − Start unit and allow 5 minutes for unit to reach steady
state.
3 − While waiting for the unit to stabilize, observe the
flame. Flame should be stable and should not lift from
burner. Natural gas should burn blue.
5 − Gas is ignited, flame sensor proves the flame, and the
combustion process continues.
6 − If flame is not detected after first ignition trial, the igni-
tion control will repeat steps 3 and 4 four more times
before locking out the gas valve (ꢀWATCHGUARD"
flame failure mode). The ignition control will then auto-
matically repeat steps 1 through 6 after 60 minutes.
4 − After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to value given in table
12.
NOTE − Shut unit off and remove manometer as soon as an
accurate reading has been obtained. Take care to remove
barbed fitting and replace threaded plug.
7 − To interrupt the 60−minute ꢀWATCHGUARD" period,
move thermostat from ꢀHeat" to ꢀOFF" then back to
ꢀHeat." Heating sequence then restarts at step 1.
Proper Combustion
Gas Pressure Adjustment
Furnace should operate a minimum 15 minutes with cor-
rect manifold pressure and gas flow rate before checking
combustion. Take combustion sample beyond the flue out-
let and compare to the tables below. The maximum car-
bon monoxide reading should not exceed 50 ppm.
Gas Flow (Approximate)
TABLE 10
GAS METER CLOCKING CHART
Seconds for One Revolution
TABLE 11
ML180UH
CO %
CO %
For L.P.
2
For Nat
2
Natural
LP
ML180UH
Unit
Unit
−045
−070
−090
−110
−135
1 cu ft
Dial
80
2 cu ft
Dial
1 cu ft
Dial
2 cu ft
DIAL
−045
−070
−090
−110
−135
160
110
82
200
136
102
82
400
272
204
164
136
7.2 − 7.8
7.5 − 9.0
55
41
33
66
27
54
68
High Altitude
Natural−1000 btu/cu ft
LP−2500 btu/cu ft
The manifold pressure may require adjustment and com-
bustion air pressure switch may need replacing to ensure
and gas conversion kits.
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
and rate is incorrect, check gas orifices for proper size and
restriction. Remove temporary gas meter if installed.
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.
NOTE − To obtain accurate reading, shut off all other gas
appliances connected to meter.
Page 30
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TABLE 12
Manifold Pressure Settings at all Altitudes
Line Pressure in.wg.
Model
Input Size
Gas
0−2000 ft
2105−4500 ft.
4501−7500 ft
7501 − 10,000 ft
Min
4.5
Max
13.0
13.0
13.0
13.0
13.0
13.0
13.0
13.0
13.0
13.0
Nat
LP/propane
Nat
3.5
10.0
3.5
3.2
10.0
3.2
3.0
10.0
2.8
3.5
10.0
3.5
045
070
090
110
135
11.0
4.5
LP/propane
Nat
10.0
3.5
10.0
3.2
10.0
2.7
10.0
3.5
11.0
4.5
LP/propane
Nat
10.0
3.5
10
9.6
10.0
3.5
11.0
4.5
3.5
3.0
LP/propane
Nat
10.0
3.5
10.0
3.5
9.6
10.0
3.5
11.0
4.5
2.9
LP/propane
10.0
10.0
9.6
10.0
11.0
TABLE 13
Pressure Switch and Gas Conversion Kits at all Altitudes
High Altitude
Natural Gas Burner
Orifice Kit
LP/Propane to
Natural Gas Burner
Orifice Kit
Natural Gas to LP/Propane
Burner Orifice Kit
High Altitude Pressure Switch Kit
Model
Input Size
0−4500 ft
4501−7500 ft
80W52
7501 − 10,000 ft
7501 − 10,000 ft
0 − 7500 ft
7501 − 10,000 ft
0 − 7500 ft
045
070
090
110
135
80W51
80W51
80W51
80W52
80W51
80W52
No Change
80W52
73W37
70W89
76W15
73W81
80W57
80W52
NOTE −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.
air temperatures have been allowed to stabilize, check the
Other Unit Adjustments
temperature rise. If necessary, adjust the blower speed to
Primary and Secondary Limits
maintain the temperature rise within the range shown on
the unit nameplate. Increase the blower speed to decrease
the temperature. Decrease the blower speed to increase
the temperature rise. Failure to adjust the temperature rise
may cause erratic limit operation.
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.
Fan Control
Flame Rollout Switches
The fan−on time of 30 seconds is not adjustable. The heat
fan−off delay (amount of time that the blower operates after
the heat demand has been satisfied) may be adjusted by
changing the jumper position across the five pins on the in-
tegrated control. The unit is shipped with a factory fan−off
delay setting of 90 seconds. The fan−off delay affects com-
fort and is adjustable to satisfy individual applications. Ad-
just the fan−off delay to achieve a supply air temperature
between 90° and 110°F at the moment that the blower is
de−energized. Longer off delay settings provide lower re-
turn air temperatures; shorter settings provide higher re-
This manually reset switches are located on the top of the
burner box.
Pressure Switch
The pressure switch is located in the heating compartment
adjacent to the combustion air inducer. The switch checks
for proper combustion air inducer operation before allow-
ing ignition trial. The switch is factory−set and requires no
adjustment.
Temperature Rise
After the furnace has been started, and supply and return
Page 31
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Blower Speeds
HEAT FAN-OFF TIME IN SECONDS
Follow the steps below to change the blower speeds.
1 − Turn off electrical power to furnace.
2 − Remove blower access panel.
NO JUMPER
3 − Disconnect existing speed tap at integrated control
speed terminal.
To adjust fan−off timing, reposition jumper across pins to
achieve desired setting.
NOTE − Termination of any unused motor leads must be
insulated.
60 Second
off Time
90 Second
off Time
120 Second
off Time
180 Second
off Time
4 − Place unused blower speed tap on integrated control
ꢀPARK" terminal or insulate.
5 − Refer to blower speed selection chart on unit wiring dia-
gram for desired heating or cooling speed. See Blower
performance data beginning on the next page.
6 − Connect selected speed tap at integrated control
speed terminal.
FIGURE 36
Thermostat Heat Anticipation
7 − Resecure blower access panel.
Set the heat anticipator setting (if adjustable) according to
the amp draw listed on the wiring diagram that is attached
to the unit.
8 − Turn on electrical power to furnace.
9 − Recheck temperature rise.
NOTE − Do not secure the electrical conduit directly to the
air ducts or structure.
Electronic Ignition
The integrated control has an added feature of an internal
Watchguard control. The feature serves as an automatic re-
set device for integrated control lockout caused by ignition
failure. This type of lockout is usually due to low gas line
pressure. After one hour of continuous thermostat demand
for heat, the Watchguard will break and remake thermostat
demand to the furnace and automatically reset the inte-
grated control to begin the ignition sequence.
Electrical
1 − Check all wiring for loose connections.
2 − Check for the correct voltage at the furnace (furnace
operating). Correct voltage is 120VAC + 10%.
3 − Check amp−draw on the blower motor with inner blow-
er panel in place.
Unit Nameplate__________Actual__________
Page 32
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BLOWER DATA
ML180UH045P24A PERFORMANCE (Less Filter)
ML180UH070P36A PERFORMANCE (Less Filter)
Air Volume / Watts at Various Blower Speeds
Air Volume / Watts at Various Blower Speeds
External
External
Medium-
High
Medium-
Low
Medium-
High
Medium-
Low
Static
Pressure
in. w.g.
Static
Pressure
in. w.g.
High
Low
High
Low
cfm Watts cfm Watts cfm Watts cfm Watts
1130 453 900 328 750 261 680 237
1115 432 885 321 735 255 670 230
1100 413 870 315 720 249 655 223
1070 396 855 304 700 241 640 217
1030 375 830 294 685 234 620 209
990 356 800 283 655 223 590 200
930 335 750 261 610 207 535 186
870 315 705 245 540 193 490 175
785 285 615 223 455 175 405 158
615 247 485 196 375 157 345 143
cfm Watts cfm Watts cfm Watts cfm Watts
1660 696 1370 604 1095 495 935 386
1620 658 1365 568 1115 468 945 374
1580 621 1355 535 1135 442 960 362
1520 595 1335 513 1130 423 955 350
1480 562 1300 478 1100 403 945 335
1400 520 1270 450 1080 382 925 320
1340 490 1205 420 1035 358 880 301
1245 458 1125 393 975 333 835 282
1160 434 1045 364 915 310 775 262
1045 393 940 334 830 283 785 268
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
ML180UH045P36A PERFORMANCE (Less Filter)
ML180UH090P36B PERFORMANCE (Less Filter)
Air Volume / Watts at Various Blower Speeds
Air Volume / Watts at Various Blower Speeds
External
External
Medium-
High
Medium-
Low
Medium-
High
Medium-
Low
Static
Pressure
in. w.g.
Static
Pressure
in. w.g.
High
Low
High
Low
cfm Watts cfm Watts cfm Watts cfm Watts
1670 711 1335 614 1140 485 925 388
1620 663 1335 577 1130 470 940 376
1570 619 1330 543 1115 455 950 366
1525 598 1315 511 1140 432 950 349
1470 552 1275 491 1125 413 945 336
1400 525 1235 455 1085 384 925 317
1330 486 1185 422 1050 361 885 300
1225 450 1135 395 995 336 840 283
1135 418 1010 359 925 315 785 258
1020 388 930 329 820 278 650 227
cfm Watts cfm Watts cfm Watts cfm Watts
1795 781 1450 606 1195 464 970 390
1760 730 1435 576 1185 452 970 378
1725 683 1420 547 1170 440 975 368
1685 656 1410 525 1170 420 980 356
1630 625 1370 501 1150 400 955 340
1535 569 1315 469 1125 391 925 326
1470 533 1275 440 1085 367 910 309
1365 490 1185 407 1020 344 840 290
1255 466 1105 380 935 314 785 266
1160 430 1000 352 815 285 680 258
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
ML180UH070P24A PERFORMANCE (Less Filter)
ML180UH090P48B PERFORMANCE (Less Filter)
External
Static
Pressure
in. w.g.
Air Volume / Watts at Various Blower Speeds
High Medium Low
Watts
Air Volume / Watts at Various Blower Speeds
External
Medium-
High
Medium-
Low
Static
Pressure
in. w.g.
High
Low
cfm
Watts
cfm
Watts
cfm
cfm Watts cfm Watts cfm Watts cfm Watts
2160 873 1825 775 1515 649 1260 544
2030 804 1780 719 1525 613 1280 518
1910 740 1740 666 1535 580 1305 493
1840 698 1705 643 1500 551 1305 474
1770 664 1635 594 1460 517 1280 445
1665 625 1560 567 1410 483 1225 420
1585 595 1470 523 1330 451 1190 391
1470 561 1365 483 1260 421 1115 368
1355 514 1230 433 1155 392 1020 338
1200 471 1120 399 1020 345 920 315
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1160
1135
1115
1085
1045
1015
965
450
439
429
410
389
374
358
335
315
289
1005
990
975
955
925
885
835
780
700
565
380
369
358
348
335
321
307
289
268
238
865
845
820
790
775
735
700
635
560
420
309
299
289
279
270
260
248
232
214
189
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
890
810
715
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BLOWER DATA
ML180UH110P48C PERFORMANCE (Less Filter)
Air Volume / Watts at Various Blower Speeds
External
Medium-
High
Medium-
Low
Static
Pressure
in. w.g.
High
Low
cfm Watts cfm Watts cfm Watts cfm Watts
2170 980 1845 792 1565 678 1270 564
2125 919 1820 747 1555 648 1300 540
2080 862 1790 705 1540 619 1335 516
2015 807 1745 652 1545 587 1335 498
1940 748 1695 629 1505 552 1320 470
1850 716 1635 581 1470 523 1295 449
1775 679 1575 560 1395 484 1235 417
1680 637 1470 508 1320 450 1170 387
1560 592 1350 469 1205 404 1050 345
1425 546 1190 424 1060 362 910 307
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
ML180UH110P60C PERFORMANCE (Less Filter)
Air Volume / Watts at Different Blower Speeds
Bottom Return Air, Side Return Air with Optional Return Single Side Return Air − Air volumes in bold require field
Air Base, Return Air from Both Sides or Return Air from fabricated transition to accommodate 20 x 25 x 1 in. air filter
External
Static
Bottom and One Side.
in order to maintain proper air velocity.
High Medium-High Medium-Low
Pressure
in. w.g.
High
Medium-High Medium-Low
Low
Low
cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts
2575 1391 2270 1050 1845 860 1430 661 2715 1509 2175 1103 1695 858 1410 653
2520 1359 2250 1034 1860 841 1455 654 2605 1454 2160 1060 1740 848 1430 651
2465 1329 2230 1018 1870 823 1480 647 2505 1401 2150 1018 1785 838 1450 649
2385 1307 2180 981 1885 809 1540 646 2435 1349 2115 991 1795 818 1485 638
2295 1256 2105 942 1865 778 1570 638 2350 1308 2070 965 1805 801 1480 631
2200 1214 2055 909 1845 762 1570 619 2260 1274 2010 929 1785 775 1480 621
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
2130 1186 1985 882 1795 741 1550 604 2175 1228 1955 901 1755 752 1490
611
2015 1150 1890 848 1720 711 1505 580 2085 1186 1850 853 1710 722 1460 594
1905 1105 1810 815 1675 687 1470 565 1965 1147 1785 818 1640 689 1425 567
1795 1054 1710 779 1545 647 1375 533 1830 1094 1700 794 1555 662 1355 545
0.90
ML180UH135P60D PERFORMANCE (Less Filter)
Air Volume / Watts at Different Blower Speeds
Bottom Return Air, Side Return Air with Optional Return Single Side Return Air − Air volumes in bold require field
Air Base, Return Air from Both Sides or Return Air from fabricated transition to accommodate 20 x 25 x 1 in. air filter
External
Static
Bottom and One Side.
in order to maintain proper air velocity.
High Medium-High Medium-Low
Pressure
in. w.g.
High
Medium-High Medium-Low
Low
Low
cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts
2785 1492 2205 1083 1665 840 1345 632 2810 1528 2185 1100 1705 835 1260 622
2750 1441 2220 1056 1725 825 1395 625 2725 1463 2180 1075 1715 827 1320 624
2720 1392 2235 1029 1785 810 1445 618 2640 1400 2180 1051 1720 819 1380 626
2605 1362 2220 1002 1820 800 1460 623 2575 1374 2165 1005 1790 803 1420 622
2495 1312 2185 968 1845 779 1485 616 2495 1343 2145 988 1775 791 1450 617
2420 1275 2135 939 1825 767 1505 605 2405 1292 2105 948 1780 777 1470 610
2335 1234 2080 909 1825 753 1495 593 2305 1257 2045 914 1775 753 1480 593
2220 1190 1995 864 1760 716 1475 576 2215 1214 1970 884 1740 727 1455 583
2120 1157 1890 835 1680 686 1435 558 2110 1170 1890 851 1675 699 1430 565
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1985 1102 1790 794 1605 656 1390 536 1985 1122 1790 811 1600 667 1380 543
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Service
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.
WARNING
ELECTRICAL SHOCK, FIRE,
OR EXPLOSION HAZARD.
Filters
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.
All ML180UH filters are installed external to the unit. Filters
should be inspected monthly. Clean or replace the filters
when necessary to ensure that the furnace operates prop-
erly. Replacement filters must be rated for high velocity air-
Flue And Chimney
When servicing controls, label all wires prior to dis-
connecting. Take care to reconnect wires correctly.
Verify proper operation after servicing.
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.
Electrical
At the beginning of each heating season, a qualified techni-
cian should check the system as follows:
1 − Check all wiring for loose connections.
2 − Check for the correct voltage at the furnace (furnace
operating). Correct voltage is 120VAC + 10%.
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.
3 − Check amp−draw on the blower motor with inner blow-
er panel in place.
Unit Nameplate__________Actual__________
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Cleaning the Heat Exchanger and Burners
NOTE − Use papers or protective covering in front of the fur-
nace during cleaning.
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.
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.
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.
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.
7 − Remove screws securing burner box and remove
burner box.
8 − NOX units only − Remove screw securing NOX insert.
ML180UH BURNER, COMBUSTION AIR INDUCER ASSEMBLY &
HEAT EXCHANGER REMOVAL
Gasket
Flue Transition
Pressure Switch
Rollout Switches
(−090, −110 −135 units)
Heat Exchanger
Rollout Switches
(−045 and −070 units)
Ignitor
Orifice Plate
Collector Box
Combustion Air Inducer
Sensor
Retention Rings
Cross Over
Manifold And Gas Valve
FIGURE 37
Page 36
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9 − Remove screws from both sides, top and bottom of
vestibule panel.
Remove 5 screws if necessary
(either side of cabinet)
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.
11 − Backwash using steam. Begin from the burner opening
on each clam. Steam must not exceed 275°F.
1
2
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
37 shows burner detail.
3
4
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.
5
14 −Reinstall heat exchanger in vestibule. (Replace the
five screws in the cabinet from step 10 if removed).
15 −NOx units only − Replace NOx inserts.
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.
17 −Reinstall burner box, manifold assembly and burner box
cover.
FIGURE 39
18 −Reconnect all wires.
ML180UH NOx INSERTS
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.
NOx Insert
25 −Repeat steps 24 and 26 until no leaks are detected.
26 −Replace access panel.
FIGURE 38
Page 37
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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: ML180UH045P24A−01. 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
Combustion air inducer
Gas valve
Integrated control
Door interlock switch
Circuit breaker
Blower Parts
Main burner cluster
Main burner orifices
Pressure switch
Ignitor
Primary limit control
Flame rollout switch (s)
Secondary limit
Blower wheel
Blower housing
Motor
Motor mounting frame
Motor capacitor
Blower housing cutoff plate
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Integrated Control Diagnostic Codes
DIAGNOSTIC CODES
Make sure to Identify LED’S Correctly.
LED #1 (Red)
LED #2 (Green)
DESCRIPTION
SIMULTANEOUS
SLOW FLASH
SIMULTANEOUS
SLOW FLASH
Power on − Normal operation.
Also signaled during cooling and continuous fan.
SIMULTANEOUS
FAST FLASH
SIMULTANEOUS
FAST FLASH
Normal operation − signaled when heating demand initiated at thermostat.
Primary or secondary limit switch open. Limit must close within 3 minutes or unit
goes into 1 hour Watchguard.
SLOW FLASH
OFF
ON
Pressure prove switch open.
SLOW FLASH
OR: Blocked inlet/exhaust vent;
OR: Pressure switch closed prior to activation of combustion air inducer.
ALTERNATING
SLOW FLASH
ALTERNATING
SLOW FLASH
Watchguard 1 hour − burners failed to ignite or lost flame 5 times during single
heating demand.
SLOW FLASH
ON
OFF
Flame sensed without gas valve energized.
SLOW FLASH
Rollout switch open. OR: 12-pin connector improperly attached.
ON
ON
ON
OFF
Circuit board failure or control wired incorrectly.
OFF
ON
FAST FLASH
SLOW FLASH
Main power polarity reversed. Switch line and neutral.
SLOW FLASH
FAST FLASH
Low flame signal. Measures below 1.5 microamps. Replace flame sense rod.
ALTERNATING
FAST FLASH
ALTERNATING
FAST FLASH
Improper main ground.
OR: Line voltage below 90 volts.
NOTE − Slow flash rate equals 1 Hz (one flash per second). Fast flash rate equals 3 Hz (three flashes per second).
Minimum flame sense current = 0.5 microAmps.
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Troubleshooting: Heating Sequence of Operation
HEATING SEQUENCE OF OPERATION
ABNORMAL HEATING MODE
NORMAL HEATING MODE
POWER ON
GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER DELAY OFF.
LED #1 ON
NO
CONTROL SELF−CHECK OKAY?
LED #2 ON
(RESET CONTROL BY TURNING MAIN POWER OFF.)
YES
NO
POLARITY REVERSED.
LED #1 −− FAST FLASH
LED #2 −− SLOW FLASH
IS POLARITY CORRECT?
YES
NO
IMPROPER GROUND.
LED #1 −− ALTERNATING FAST FLASH
LED #2 −− ALTERNATING FAST FLASH
IS THERE A PROPER GROUND?
YES
NO
LEDs SIGNAL FAST ALTERNATING FLASH.
CONTROL WILL NOT RESPOND TO A CALL FOR
HEATING UNTIL VOLTAGE RISES ABOVE 95 VOLTS.
IS VOLTAGE
ABOVE 90 VOLTS?
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.
INDOOR BLOWER ON.
LED #1 −− ON. LED #2 −− SLOW FLASH.
YES
NO
ROLLOUT SWITCH CLOSED?
SEQUENCE HOLDS UNTIL ROLLOUT SWITCH CLOSES
AND POWER IS RESET OR T’STAT IS INTERRUPTED
FOR MINIMUM OF 1 SECOND.
YES
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.
INDOOR BLOWER ON HEATING SPEED.
LED #1 −− SLOW FLASH
NO
BURNER OFF?
(Flame sensed without gas valve energized)
LED #2 −− OFF
YES
NO
NORMAL OPERATION:
LED #1 −− SLOW FLASH
LED #2 −− SLOW FLASH
YES
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER ON
LED #1 SLOW FLASH RATE
LED #2 −− ON
THERMOSTAT CALLS FOR HEAT:
LED #1 −− FAST FLASH
LED #2 −− FAST FLASH
NO
YES
PRIMARY AND SECONDARY LIMIT SWITCH.
CLOSED?
GAS VALVE OFF.
COMBUSTION AIR INDUCER OFF.
YES
INDOOR BLOWER OFF WITH DELAY.
LED #1 OFF
LED #2 SLOW FLASH
NO
IS COMBUSTION AIR
PRESSURE SWITCH OPEN?
(Sequence holds until pressure switch
opens or thermostat resets control.)
YES
IS COMBUSTION AIR INDUCER
ENERGIZED?
YES
PRESSURE SWITCH IS IN WATCHGUARD MODE.
GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF WITH DELAY.
YES
NO
HAS COMBUSTION AIR PRESSURE
SWITCH CLOSED IN 2.5 MINUTES?
LED #1 −− OFF. LED #2 −− SLOW FLASH.
IS 5-MINUTE RESET PERIOD COMPLETE?
YES
CONTINUED NEXT PAGE
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Troubleshooting: Heating Sequence of Operation (Continued)
HEATING SEQUENCE CONTINUED
NORMAL HEATING MODE
ABNORMAL HEATING MODE
15-SECOND COMBUSTION AIR INDUCER PREPURGE
INITIATED BY CLOSED PRESSURE SWITCH.
LEDS SIGNAL
ALTERNATING
YES
NO
NO
FAST FLASH UNTIL
VOLTAGE IS ABOVE
95 VOLTS, THEN
RESTARTS HEATING
SEQUENCE.
IS VOLTAGE ABOVE 90 VOLTS?
IGNITOR WARM-UP −− 20 SECONDS.
YES
YES
4-SECOND TRIAL FOR IGNITION.
GAS VALVE OPENS. IGNITOR ENERGIZED FOR
FIRST 3 SECONDS OF THE TRIAL.
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.
INDOOR BLOWER OFF.
HAS CONTROL FAILED TO SENSE FLAME FOR
FIVE CONSECUTIVE TRIES DURING A SINGLE
HEAT DEMAND?
YES
NO
NO
FLAME STABILIZATION PERIOD.
4 SECONDS
YES
FLAME RECTIFICATION CURRENT
CHECK. CAN FLAME BE PROVEN WITHIN
4 SECONDS AFTER GAS VALVE OPENS?
(0.5 microamps)
WATCHGUARD MODE. GAS VALVE OFF.
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF WITH DELAY
LEDs SIGNAL WATCHGUARD FAILURE CODE.
IS 60-MINUTE RESET PERIOD COMPLETE?
YES
YES
NO
NO
YES
HAS CONTROL RESET IGNITION
SEQUENCE FOUR TIMES?
FLAME PRESENT?
YES
LIMIT SWITCH WATCHGUARD
MODE. GAS VALVE, COMB. AIR
INDUCER AND INDOOR BLOW-
ER OFF. LEDs SIGNAL LIMIT
SWITCH OPEN UNTIL MAIN
POWER IS
LOW FLAME SIGNAL
(Does not affect operation of control)
LED #1 −− SLOW FLASH
NO
FLAME SIGNAL 1.5 MICROAMPS OR GREATER?
YES
LED #2 −− FAST FLASH
INDOOR BLOWER ON
AFTER 30−SECOND DELAY
INTERRUPTED OR
T’STAT IS CYCLED
GAS VALVE DE−ENERGIZED.
COMBUSTION AIR INDUCER DE−ENERGIZED.
YES
OFF/ON FOR 1 SEC.
MINIMUM. 60−MINUTE
WATCHGUARD PE-
RIOD STARTS AT
TIME LIMIT CLOSES.
IS 60−MIN. PERIOD
COMPLETE?
INDOOR BLOWER ON UNTIL SWITCH CLOSES.
LED #1 −− SLOW FLASH. LED #2 −− ON.
IS LIMIT SWITCH CLOSED?
NO
PRIMARY AND SECONDARY LIMIT
SWITCHES CLOSED?
YES
YES
HAS PRIMARY / SECONDARY
LIMIT RESET TIME
EXCEEDED 3 MINUTES?
YES
NO
GAS VALVE POWER OFF.
NO
COMBUSTION AIR INDUCER POWER ON.
INDOOR BLOWER ON
LED #1 −− ON. LED #2 −− SLOW FLASH.
ROLLOUT SWITCH CLOSED?
YES
SEQUENCE HOLDS UNTIL ROLLOUT SWITCH IS RESET
AND MAIN POWER IS INTERRUPTED OR
THERMOSTAT IS CYCLED OFF/ON FOR 1 SEC. MINIMUM.
NO
COMBUSTION AIR PRESSURE
SWITCH CLOSED?
YES
HAS PRESSURE SWITCH OPENED 5
TIMES IN THE SAME HEAT DEMAND?
NO
1 HR
PRESSURE
SWITCH
THERMOSTAT DEMAND SATISFIED.
YES
WATCHGUARD
MODE
YES
GAS VALVE DE−ENERGIZED.
COMBUSTION AIR INDUCER ON.
LED #1 & #2 SIMULTANEOUS SLOW FLASHES.
INDOOR BLOWER OFF WITH DELAY
LED #1 −− OFF. LED #2 −− SLOW FLASH.
HAS CAB SWITCH CLOSED IN 2.5 MINUTES?
YES
COMB. AIR INDUCER CONTINUES 5-SECOND
POST PURGE AFTER T’STAT DEMAND IS SATISFIED.
INDOOR AIR BLOWER COMPLETES SELECTED ꢀOFF"
DELAY BEFORE SHUTTING OFF.
NO
5-MINUTE PRESSURE SWITCH
WATCHGUARD MODE.
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Troubleshooting: Cooling Sequence of Operation
COOLING SEQUENCE OF OPERATION
NORMAL COOLING MODE
ABNORMAL COOLING MODE
POWER ON
IGNITION CONTROL MAIN POWER ON.
GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF WITH NORMAL DELAY.
SIGNAL CIRCUIT BOARD FAILURE AT LED.
NO
CONTROL SELF DIAGNOSTIC CHECK.
IS CONTROL OPERATING NORMALLY?
INTERRUPT MAIN POWER TO RESET CONTROL.
YES
NO
SIGNAL IMPROPER GROUND AT LED.
CONTROL WILL CONTINUE TO CALL FOR COOLING
IN THIS CONDITION.
IS THERE A PROPER GROUND?
YES
SIGNAL POLARITY REVERSED AT LED. CONTROL
WILL CONTINUE TO CALL FOR COOLING IN THIS
CONDITION.
NO
IS POLARITY CORRECT?
YES
NO
LED SIGNALS LOW VOLTAGE. CONTROL WILL
CONTINUE TO CALL FOR COOLING
IN THIS CONDITION.
IS VOLTAGE
ABOVE 90 VOLTS?
YES
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.
INDOOR BLOWER ON.
NO
ROLLOUT SWITCH MONITORED CONTINUOUSLY.
IS ROLLOUT SWITCH CLOSED?
SIGNAL ROLL-OUT SWITCH OPEN AT LED.
SEQUENCE HOLDS UNTIL ROLLOUT SWITCH CLOSES
AND MAIN POWER IS INTERRUPTED OR THERMOSTAT
IS CYCLED OFF/ON FOR 1 SEC. MINIMUM.
YES
LED: SLOW FLASH RATE REMAINS UNCHANGED
THROUGHOUT COOLING CYCLE.
THERMOSTAT CALLS FOR COOLING.
COMPRESSOR CONTACTOR AND SYSTEM FAN
ENERGIZED WITH 2-SECOND DELAY
(COOLING SPEED). EAC TERM. ENERGIZED.
THERMOSTAT OPENS.
COMPRESSOR OFF.
SYSTEM FAN AND EAC TERM. OFF
WITH 45-SECOND DELAY.
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Troubleshooting: Continuous Fan Sequence of Operation
CONTINUOUS HEAT SPEED FAN SEQUENCE OF OPERATION
LED: SLOW FLASH RATE REMAINS
UNCHANGED THROUGHOUT SEQUENCE.
MANUAL FAN SELECTION MADE AT THERMOSTAT.
CONTROL (G) ENERGIZES SYSTEM FAN AT HEAT
SPEED. EAC TERMINAL IS ENERGIZED.
HUM TERM. ENERGIZES
WITH COMB. AIR INDUCER.
THERMOSTAT CALLS FOR HEAT (W).
YES
NO
SYSTEM FAN REMAINS ON
HEATING SPEED.
THERMOSTAT CALLS FOR COOLING.
YES
NO
SYSTEM FAN SWITCHED TO COOL SPEED.
EAC TERM. REMAINS ON.
THERMOSTAT OPENS.
HUM TERM. DE−ENERGIZES
WITH COMB. AIR INDUCER
THERMOSTAT OPENS.
MANUAL FAN SELECTION MADE AT THERMOSTAT.
CONTROL (G) ENERGIZES SYSTEM FAN AT HEAT
SPEED. EAC TERM. ENERGIZED.
SYSTEM FAN REMAINS ON
HEATING SPEED.
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