21D83M-843
Integrated Single Stage
Furnace Control Replacement Kit
INSTALLATION INSTRUCTIONS
FAILURETO READ AND FOLLOW ALL INSTRUCTIONS CAREFULLY BEFORE
INSTALLING OR OPERATING THIS CONTROL COULD CAUSE PERSONAL
INJURY AND/OR PROPERTY DAMAGE.
DESCRIPTION
The 21D83M-843 kit will replace the following Controls:
Kit includes:
1 – 50A66-843 ignition control board
1 – Wiring harness (9-pin to 12-pin)
1 – Wiring harness (4-pin to 6-pin)
1 – Mounting panel
4 – Stand-off fasteners
1 – Circuit breaker
Lennox
White-Rodgers Page
Reference
10M9301 32M8801 50A65-120
3
4
5
PROCEDURE 1
Figure 1, Picture
1, Table 1, Wiring
Diagram 5001-6973
12L6901
56L8401 50A65-121
24L8501
63K8901
97L4801
50A62-120
50A62-121
50A62-820
PROCEDURE 2
Figure 1, Picture
2, Table 2, Wiring
Diagram 5001-6972
1 – 4" blue wire
2 – Wiring diagrams
The kit includes the 50A66-843 which is an automatic gas
interruptedignitioncontrolthatemploysamicroprocessor
to continually monitor, analyze, and control the proper
operation of the gas burner, inducer, and fan.
100925-01 30W2501 21D83M-843
100925-03 69M0801 50A66-122
17W9201 69M1501 50A66-123
23W5101 83M00
PROCEDURE 3
Thesecontrolsincorporatesystemfaultanalysisforquick
gas flow shut-off, coupled with automatic ignition retry
upon sensing a fault correction.
Follow instructions for replacement of your model num-
ber under the heading INSTALLATION.
PRECAUTIONS
Installation should be done by a qualified heating and air
conditioning contractor or licensed electrician.
If in doubt about whether your wiring is millivolt, line, or
low voltage, have it inspected by a qualified heating and
air conditioning contractor or licensed electrician.
Do not exceed the specification ratings.
WARNING
Failure to comply with the following warnings
couldresultinpersonalinjuryorpropertydamage.
FIRE HAZARD
• Do not exceed the specified voltage.
• Replace existing control with exact model
and dash number.
• Protect the control from direct contact with
water (dripping, spraying, rain, etc.).
• If the control has been in direct contact with
water, replace the control.
• Label all wires before disconnection when
servicing controls. Wiring errors can cause
improper and dangerous operation.
• Route and secure wiring away from flame.
SHOCK HAZARD
• Disconnect electric power before servicing.
• Ensure proper earth grounding of appliance.
!
All wiring must conform to local and national electrical
codes and ordinances.
This control is a precision instrument, and should be
handled carefully. Rough handling or distorting compo-
nents could cause the control to malfunction.
Followinginstallationorreplacement,followmanufacturer’s
recommended installation/service instructions to ensure
proper operation.
CAUTION
!
Donotshortoutterminalsongasvalveorprimary
control. Short or incorrect wiring may damage
the thermostat.
• Ensure proper connection of line neutral and
line hot wires.
EXPLOSION HAZARD
• Shut off main gas to appliance until installa-
tion is complete.
PART NO. 37-7337B
Replaces 37-7337A
1244
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INSTALLATION
PROCEDURE 1
WARNING
!
FIRE HAZARD
REPLACING 10M9301, 12L6901, 32M8801,
50A65-120, 50A65-121 or 56L8401
• Do not exceed the specified voltage.
• Replace existing control with exact model and
dash number.
• Protect the control from direct contact with water
(dripping, spraying, rain, etc.).
Mounting panel
• If the control has been in direct contact with water,
replace the control.
• Label all wires before disconnection when servic-
ingcontrols.Wiringerrorscancauseimproperand
dangerous operation.
Circuit breaker
in series between
Pin 3 and
• Route and secure wiring away from flame.
Transformer (TH)
SHOCK HAZARD
• Disconnect electric power before servicing.
• Ensure proper earth grounding of appliance.
• Ensure proper connection of line neutral and line
Optional 4" blue
wire to connect to
Transformer (TH)
hot wires.
EXPLOSION HAZARD
• Shut off main gas to appliance until installation is
complete.
Photo 1
1. Disconnect all electrical power and shut off the gas
supply to the furnace.
2. Remove the access panel.
3. Disconnect wiring and remove existing ignition
control board from the control box.
4. Install provided circuit breaker in unit control box
or secure circuit breaker to a wire harness using
wire ties.
CAUTION
Do not short out terminals on gas valve or primary
control. Short or incorrect wiring may damage the
thermostat.
!
MOUNTING PANEL
5. Position the provided mounting panel with the
arrow on the front of the panel pointing up. Position
the replacement 50A66-843 ignition control board
over the holes marked "A" in figure 1. Insert the
replacement control stand-off fasteners into the
holes in the mounting panel.
TheMountingPanelisrequiredinProcedure1andProce-
dure 2.It will become part of the installation for Procedure
1. It will be used as a template for locations to drill holes
in Procedure 2, Step 4A and 4B. It will become part of
the installation in Procedure 2, Step 4C.
6. Insert the four provided stand-off fasteners into the
back of the mounting panel in the holes marked "B"
in figure 1. Insert the replacement control board
assembly into the existing holes in the control box
or blower panel.
7. Insert provided circuit breaker in series between the
blue transformer wire connecting position 3 on the
12-pin connector to the transformer (TH), optional 4"
blue wire provided for transformers that have a quick-
connect terminal.
B
A
B
A
C
C
Arrow on
front of panel
8. Connect the remaining 120 VAC hot and neutral wires
and the flame sense wire to the replacement control
per table 1, page 4.
9. Affix wiring diagram 5001-6973 adjacent to the
existing unit wiring diagram.
B
B
C
C
A
A
10. Replace the access panel.
Figure 1 – Mounting Panel
11. Restore the electrical power and gas supply. Refer
to the furnace installation instructions for start-up
and check-out procedures.
3
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INSTALLATION
over the marks. Use the mounting panel
as a template to drill 3/16" holes through
each of the holes marked "A". Install the
replacement control in the freshly drilled holes
inthebloweraccesspanel.Usealuminumtape
to seal the unused holes.
TABLE 1
Type
Existing
Replacement
Control Board
COOL
Control Board
COOL-H
HEAT-H
PARK (2)
EAC-H
HEAT
PARK (2)
EAC
LINE
XFMR
B. When replacing original 63K8901 board in
downflow applications – Look at the existing
control board holes as if the unit were installed
in the upflow position. Make a mark 5/8"
ABOVE each of the existing mounting holes.
Position the provided mounting panel so that
the holes marked "C" in figure 1, page 3 are
over the marks. Use the mounting panel as a
template to drill 3/16" holes through each of
the holes marked "A". Install the replacement
control in the freshly drilled holes in the blower
access panel. Use aluminum tape to seal the
unused holes.
C. All other units – Position the provided
mounting panel so that the arrow on the
front of the panel is pointing up. Position the
replacement 50A66-843 ignition control board
over the holes marked "A" in figure 1, page 3.
Insert the replacement control stand-off
fasteners into the holes in the mounting panel.
80UHG, 90UGF, G23, G26, GHR26, G32,
GHR32, G40, G41, G50, G51, G60 and G61
units – Insert the four provided stand-off
fasteners into the back of the mounting panel in
the holes marked "B" in figure 1. 80MGF, G24M
and G27M units – Insert the four provided
stand-off fasteners into the back of the mounting
panel into the holes marked "C" in figure 1.
Insert the replacement control board assembly
into the existing holes in the control box or
blower panel.
L1
120 VAC
LINE-H
XFMR-H
HUM-H
NONE
LINE-N
HUM-N
EAC-N
XFMR-N
CIR-N
E33
HUM
FAN
Neutral
120 VAC
(5)
Neutral
120 VAC
Flame Sense
FS
PROCEDURE 2
REPLACING 24L8501, 50A62-120, 50A62-121,
50A62-820, 56L8301, 63K8901 or 97L4801
Mounting panel
Wiring harness
(4-pin to 6-pin)
GND
Transformer
Circuit breaker
in series between
5. Insert provided circuit breaker in series between
the blue wire on Pin 3 of the wiring harness (9-pin
to 12-pin) and the blue transformer wire. Optional
4" blue wire provided for transformers that have a
quick-connect terminal.
Wiring harness
Pin 3 and Trans-
(9-pin to 12-pin)
former (TH)
Optional 4" blue
wire to connect to
Transformer (TH)
6. Connect the provided 9-pin to 12-pin wiring
harness to the unit 9-pin connector.
Photo 2
7. Connect the provided 4-pin to 6-pin wiring harness
to the unit 6-pin connector.
1. Disconnect all electrical power and shut off the gas
supply to the furnace.
8. Connect the yellow wire from position 6 on the 12-
pin connector to the yellow transformer wire.
9. Connect GND wire to equipment ground.
10. Connect the remaining 120 VAC hot and neutral
wires and the flame sense wire to the replacement
control per table 2, page 5 .
11. Affix wiring diagram 5001-6972 adjacent to the
existing unit wiring diagram
12. Replace the access panel.
2. Remove the access panel.
3. Disconnect wiring and remove existing ignition
control board from the control box.
4. A. When replacing original 63K8901 board
in upflow or horizontal applications or
downflow applications – Look at the existing
control board holes as if the unit were installed
in the upflow position. Make a mark 1" to the
right of each of the existing mounting holes.
Position the provided mounting panel so that
13. Restore the electrical power and gas supply. Refer
to the furnace installation instructions for start-up
and check-out procedures.
the holes marked "C" in figure 1, page 3 are
4
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INSTALLATION
PROCEDURE 3
TABLE 2
Type
Existing
Control Board
Replacement
Control Board
REPLACING 100925-01, 100925-02,
ACB COOL
ACB HEAT
PARK M1
PARK M2
ACC
COOL
HEAT
PARK
PARK
EAC
100925-03, 17W9201, 23W5101,
30W2501, 50A66-122, 50A66-123,
69M0801 or 69M1501
1. Disconnect all electric power and shut off gas
supply to the furnace.
2. Remove the access panel
3. Disconnect wiring and remove existing ignition
control board.
4. Insert the replacement board into existing holes.
5. Reconnect wiring.
L1
120 VAC
120 VAC HOT
120 VAC TX
HTG ACC
ACB LOW
LINE
XFMR
HUM
FAN
Neutral
120 VAC
Neutral 120 VAC
Return (5)
Neutral
120 VAC (5)
6. Replace access panel.
Flame Sense
E33
FS
7. Restore the electrical power and gas supply. Refer
to the furnace installation instructions for start-up
and check-out procedures.
OPERATION
goes into retry mode. For the second attempt to ignite
gas within the same call for heat, the control increases
the ignitor temperature to the value it was on the third
previous successful ignition. After ignition is successful,
the control sets the ignition temperature at this value for
the next 255 calls for heat, after which the control repeats
the adaptive algorithm. The control is constantly making
adjustments to the ignitor temperature to compensate for
changes in the line voltage.
OPTION SWITCHES
The option switches on the 50A66-843 control are used
to determine the length of the heat delay-to-fan-off and
cool-delay-to-fan-off periods. The following table shows
the time periods that will result from the various switch
positions.
OPTION SWITCH POSITIONS
HEAT delay-
to-fan-off:
Set switch
The 80 VAC Silicon Nitride ignitor manufactured by
White-Rodgers must be used. These ignitors are spe-
cially designed to operate with the 50A66-843's adap-
tive ignition routine to ensure the most efficient ignitor
temperature.
#1
#2
60 sec.
90 sec.*
120 sec.
180 sec.
Off
Off
On
On
Off
On
Off
On
At the end of the ignitor warm-up time, both valves in the
gas valve are opened. Flame must be detected within 4
seconds.
COOL delay-
to-fan-off:
Set switch
#3
2 sec.
45 sec.*
Off
On
If flame is detected, the delay-to-fan-on period begins.
After the delay-to-fan-on period ends, the circulator fan is
energized at heat speed. If there is an optional electronic
air cleaner on the system, the electronic air cleaner and
the humidifier are energized. When the thermostat is
satisfied, the gas valve is de-energized. After proof of
flameloss, theinducerblowerremainsenergizedtopurge
the system for 5 seconds and the delay-to-fan-off period
begins. When the purge is complete, the inducer blower
andhumidifierarede-energized.Afterthedelay-to-fan-off
period ends, the circulator fan and electronic air cleaner
*Factory Setting
HEAT MODE
In a typical system, a call for heat is initiated by closing the
thermostat contacts. This starts the 50A66-843 control’s
heating sequence.The inducer blower and humidifier are
energized. After a 15-second pre-purge period, the 768A
Silicon Nitride ignitor is powered.
This controller has an adaptive algorithm that reduces are de-energized.
ignitor temperature to slightly greater than the minimum
If flame is not detected, both valves are de-energized,
temperature required to ignite gas in each particular
application. The control measures the line voltage and
determines an initial ignitor temperature setting based
on the measurement. After each successful ignition, the
control lowers the ignitor temperature slightly for the next
ignition attempt.The control continues to lower the ignitor
temperature until ignition does not occur, and the control
the ignitor is turned off, and the 50A66-843 control goes
into the“retry”sequence.The“retry”sequence provides a
15-secondwaitfollowinganunsuccessfulignitionattempt
(flame not detected).After this wait, the ignition sequence
is restarted. If this ignition attempt is unsuccessful, three
more retries will be made before the control goes into
system lockout.
5
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OPERATION
If flame is detected, then lost, the 50A66-843 control will
repeat the initial ignition sequence for a total of three
"recycles". After three unsuccessful "recycle" attempts,
the control will go into system lockout.
COOL MODE
In a typical system, a call for cool is initiated by closing
the thermostat contacts. This energizes the 50A66-843
control's cooling sequence.The compressor is energized
and the delay-to-fan-on period begins. After the delay-
to-fan-on periods ends, the circulator fan is energized at
cool speed. The electronic air cleaner (optional) is also
energized. After the thermostat is satisfied, the compres-
sorisde-energizedandthedelay-to-fan-offperiodbegins.
After the delay-to-fan-off period ends, the circulator fan
and electronic air cleaner (optional) are de-energized.
If flame is established for more than 10 seconds after igni-
tion,the50A66-843controllerwillcleartheignitionattempt
(or retry) counter. If flame is lost after 10 seconds, it will
restart the ignition sequence.This can occur a maximum
of four times before system lockout.
A momentary loss of gas supply, flame blowout, or a
shorted or open condition in the flame probe circuit will be
sensed within 2 seconds. The gas valve will de-energize
andthecontrolwillrestarttheignitionsequence.Recycles
will begin and the burner will operate normally if the gas
supply returns, or the fault condition is corrected, before
the last ignition attempt. Otherwise, the control will go
into system lockout.
MANUAL FAN ON MODE
If the thermostat fan switch is moved to the ON position,
the circulator fan (heat speed) and optional electronic air
cleaner are energized. When the fan switch is returned
to the AUTO position, the circulator fan and electronic air
cleaner (optional) are de-energized.
If the control has gone into system lockout, it may be pos-
sible to reset the control by a momentary power interrup-
tionoftensecondsorlonger.RefertoPRECAUTIONARY,
SYSTEM LOCKOUT, AND DIAGNOSTIC FEATURES.
SYSTEM LOCKOUT AND DIAGNOSTIC FEATURES
2. Interrupt the 24 VAC power at the control for at least
SYSTEM LOCKOUT FEATURES
ten seconds. You may also need to reset the flame
rollout sensor switch.
Whensystemlockoutoccurs,thegasvalveisde-energized.
The circulator blower is energized at heat speed for some
faults, and if flame is sensed, the inducer blower is en-
ergized. The diagnostic indicator light will flash or glow
continuously to indicate system status. (System lockout
will never override the precautionary features.)
3. Afteronehourinlockout,thecontrolwillautomatically
reset itself.
DIAGNOSTIC FEATURES
To reset the control after system lockout, do one of
the following:
The 50A66-843 control continuously monitors its own
operation and the operation of the system. If a failure oc-
curs, the DS 1 (red) and DS 2 (green) LEDs will indicate
a failure code as shown on next page.
1. Interrupt the call for heat at the thermostat for at least
onesecond,butlessthan20seconds(ifflameissensed
with the gas valve de-energized, interrupting the call
for heat at the thermostat will not reset the control).
6
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TROUBLESHOOTING
DIAGNOSTIC TABLE
DS 1 (Red)
DS 2 (Green)
Error/Condition
Comments/Troubleshooting
Simultaneous
Simultaneous slow
Normal operation
No fault
slow flash
flash
Simultaneous
fast flash
Simultaneous
fast flash
Normal operation with call Normal operation
for heat
Slow flash
On
Open limit switch
Verify continuity through rollout switch circuit
Off
Slow flash
Pressure switch stuck
closed/open
Pressure switch stuck closed. Check switch func-
tion, verify inducer is turning off.
Pressure switch stuck open. Check pressure switch
function and tubing. Verify inducer is turning on and
pulling sufficient vacuum to engage switch.
Alternate
slow flash
Alternate slow flash External lockout (retries)
Failure to sense flame is often caused by carbon
deposits on the flame sensor, a disconnected or
shorted flame sensor lead or a poorly grounded
furnace. Carbon deposits can be cleaned with em-
ery cloth. Verify sensor is not contacting the burner
and is located in a good position to sense flame.
Check sensor lead for shorting and verify furnace
is grounded properly.
Slow flash
Off
Flame sensed with gas
valve de-energized
Verify the gas is operating and shutting down prop-
erly. Flame in burner assembly should extinguish
promptly at the end of the cycle. Check orifices and
gas pressure.
On
On
Slow flash
Open rollout switch
Verify continuity through rollout switch circuit.
On
Module – internal fault
condition
Module contacts for gas valve not operating or
processor fault. Reset control, if condition persists,
replace module.
Slow flash
Fast flash
Low flame sense current
Low flame sense current is often caused by carbon
deposits on the flame sensor, a poorly grounded
furnace or a mis-aligned flame sense probe.
Carbon deposits can be cleaned with emery cloth.
Check or improve furnace and module ground.
Verify sensor is located in or very near flame as
specified by the appliance manufacturer.
Fast flash
Slow flash
Grounding or reversed
polarity
Verify the control and furnace are properly ground-
ed. Check and reverse polarity (primary) if incorrect.
Alternate fast
flash
Alternate fast flash
Module ignitor contact
failure
Fault code indicates the module ignitor contacts
are not functioning properly. Replace module.
7
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White-Rodgers is a business
of Emerson Electric Co.
The Emerson logo is a
trademark and service mark
of Emerson Electric Co.
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