Page 1
TROUBLESHOOTING
WARNING
!
WARNING
!
GUIDE
Failure to read and follow all
instructions carefully before installing or operating this control,
could cause personal injury and/
or property damage.
INTEGRATED FURNACE
CONTROL MODULE
50A55 INTEGRATED FURNACE CONTROL MODULE
Qualied Serviceman’s Troubleshooting Guide
TROUBLESHOOTING PROCEDURE
If the light on the module is on continuously, the fault is likely to be internal to the
module. To make sure, interrupt line or 24 volt thermostat power for a few seconds
and then restore. If internal fault is indicated again, and ame sensor is not shorted
to ground, replace control. A ashing light indicates the problem is most likely in the
external components or wiring. Proceed as follows:
Turn power off before any troubleshooting or servicing begins.
Line voltage (120 VAC) could be present on the surface of the ignitor, if the system is not correctly wired. Such voltage can cause serious injury or death.
The following steps must be performed rst before any troubleshooting begins.
1) Disconnect electric power to system at main fuse or circuit breaker.
2) Visually inspect equipment for apparent damage. Check wiring for loose
connections.
3) Check for proper grounding and reversed polarity.
A. Check continuity for C terminal on module to electrical service ground and
connection at the furnace junction box. If ground connection is open, check
module ground connection and the electrical service ground connection.
Repair and retest.
B. Re-connect electric power to system.
C. Check for voltage between the line neutral terminal and furnace ground. If
voltage exists, the main power supply lines are improperly connected to the
furnace (REVERSED POLARITY). Again disconnect electric power to system;
then reverse incoming supply leads to furnace. Repeat step.
D. Recheck system for proper operation.
If neither apparent damage, loose connection nor reversed polarity is the problem,
proceed to troubleshooting chart or fault index chart that is suggested by the actual
condition.
NOTE: This troubleshooting guide is not for 50A55-4XX modules found on Trane
equipment or 50A55-1XX modules found on Lennox equipment.
FAULT INDEX CHART
No manual fan ............................................ 1A - 1K
Power supply and voltage .......................... 1C - 1G
No fan at cooling speed .............................. 2A - 2L
No induced draft motor ............................... 3A - 3H
LED ashing 2X without inducer................. 3E
LED ashing 3X with inducer...................... 3I - 3O
Ignitor does not glow .................................. 4A - 4D
Burner does not stay lit ............................... 4E - 4N
Gas supply problem.................................... 4F - 4K
No outlet pressure ...................................... 4H - 4J
Gas valve does not energize ...................... 4L - 4N
Flame sensor fault ...................................... 5A - 5P
Burner ground............................................. 5K
Polarity check ............................................. 5L - 5M
Ignitor stays on after burner ignition ........... 5B - 5C
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TECHNICAL HELPTECHNICAL HELP
259
Page 2
Place
thermostat
fan switch in
the ON
position.
Return fan
switch to
AUTO position.
Indoor Blower
Check
Does indoor
blower run at
HEAT speed?
YES
YES
NO
NO
YES
NO
YES
NO
YES
NO
Indoor blower
fault. Repair or
replace. Check
operation.
Is 24V
present at
control
terminals
G & C?
Is 120V
present at
control terminals
COOL & CIR
NEUTRAL?
Is 24V
present at
control
terminals
R & C?
Does LED
flash 1 time
when disconnect
is turned
ON?
Is 120V
present across
primary of control
transformer?
Is 24V
present across
secondary of
transformer?
Is 24V
present
across 12-pin
connector pins TH
& TR on the
control?
Is 120V
present at
control terminals
XFMR & XFMR
NEUTRAL?
Is 120V
present across
control terminals
LINE & LINE
NEUTRAL?
Repair wiring
from control to
thermostat. Check
operation.
Repair wiring
and/or plug
connection. Check
operation.
Replace
transformer. Check
operation.
Repair wiring to
transformer. Check
operation.
Correct 120V
power supply. Check
operation.
Replace control.
Check operation.
Replace control.
Check operation.
1A 1B
1E1D1C 1F
1I1H1G 1J 1K
YES
NO
YES
NO
YES
NO
YES
NO
YES
NO
WARNING
!
INTEGRATED FURNACE
CONTROL MODULE
CHART 1
TROUBLESHOOTING
GUIDE
TECHNICAL HELP
If diagnostic indicator (LED)
shows continuous flashing, turn
off gas supply at source before
disconnecting electrical power!
260
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Page 3
TROUBLESHOOTING
Place thermostat
system switch in
cooling mode and fan
switch in AUTO
position. Lower
temperature selection
lever to call for a
cooling cycle. R & Y
contacts close.
Return thermostat
to desired
setting.
With door
switch closed,
jumper control
terminals
R & Y.
Cooling
Cycle
Check
Does indoor
blower energize
at cooling
fan speed?
YES
YES
NO
NO
YES
NO
YES
NO
Repair low
voltage wiring to
thermostat. Check
operation.
Does
indoor blower
energize at
cooling fan
speed?
Is
thermostat terminal
Y connected to furnace
terminal Y?
Does
indoor blower
energize at
heating fan
speed?
Is 120V present
at primary of
transformer?
Is 24V
present at
control terminals
G & C?
Is 24V
present across
control terminals
Y & C?
Replace control.
Check operation.
Replace
transformer.
Check operation.
Repair wiring
between control and
transformer
primary. Check
operation.
Correct 120V
power supply to
control. Check
operation.
Repair low
voltage wiring to
thermostat.
Check operation.
Correct wiring
from thermostat
terminal Y to Y on
furnace. Check
operation.
YES
Indoor blower
fault. Repair or
replace motor.
Check operation.
NO
Is 120V
present at
control terminals
COOL & CIR
NEUTRAL?
2A 2B
2E
2D2C 2F
2H
2K2J
2G
YES
NO
YES
YES
YES
NO
NO
Is 120V
present at
control terminals
LINE & LINE
NEUTRAL?
2L
YES
Repair low
voltage wiring
from transformer to
control. Check
operation.
NO
Is 24V
present at
control terminals
R & C?
2I
NO
WARNING
!
GUIDE
INTEGRATED FURNACE
CONTROL MODULE
CHART 2
www.white-rodgers.com
If diagnostic indicator (LED)
shows continuous flashing, turn
off gas supply at source before
disconnecting electrical power!
TECHNICAL HELP
261
Page 4
Inducer Draft Motor
and
Pressure Switch
Check
Is induced
draft motor
energized?
YES
YESNO
Is diagnostic
LED flashing 3
times?
Call for heat.
Thermostat
contacts
R & W close.
Jumper
pressure
switch.
Disconnect
electric power
at fuse or
circuit breaker.
Is pressure
switch welded
closed?
Correct blocked
or incorrectly
installed vent.
Check operation.
Repair leaks in
inducer assembly or
replace induced
draft motor. Check
operation.
Check inducer
wiring. If OK,
repair or replace
inducer motor.
Check operation.
Replace pressure
switch. Energize
system. Check
operation.
NO
YES
NO
NO
3A 3F
Is diagnostic
LED flashing 2
times?
3B
3C
3D
3G
3H
3E
3I
3J
3L
YES
NO
Is
pressure
greater than
pressure switch
specs?
YES
Replace pressure
switch. Check
operation.
NO
Is
pressure
greater than
pressure switch
specs?
YES
YES
NO
Does ignitor
glow?
Test for
continuity across
pressure switch.
Place incline
manometer in
series with
pressure switch
tubing.
Remove vent
connector
from furnace
flue collar.
3K
WARNING
!
INTEGRATED FURNACE
CONTROL MODULE
CHART 3
TROUBLESHOOTING
GUIDE
TECHNICAL HELP
262
If diagnostic indicator (LED)
shows continuous flashing, turn
off gas supply at source before
disconnecting electrical power!
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Page 5
Main Burner
Ignition Check.
Inducer ON.
Does ignitor
warm up and
glow?
YES YES
NONO
Does burner
ignite?
Turn power OFF to furnace.
Unplug ignitor from wire
harness. Connect voltmeter
across ignitor wiring
harness leads from
control. Energize
system.
Turn manual knob to
OFF position. Connect
manometer to outlet
pressure tap. Turn knob
to ON position.
Energize system.
Is 120V
present at
control terminals
IGN & IGN
NEUTRAL?
Replace control
module. Check
operation.
Replace gas
valve. Energize
system. Check
operation.
NO
YES
NO
Repair or
replace broken
leads to gas valve.
Check operation.
4A 4E
4B
YES
Is gas
valve manual
knob in ON
position?
4F
4C
4G
4H
4K
4N
4I
4L
4M
YES
YES
Is 24V
detected
across gas
valve leads after
ignitor warm-
up time?
Is 24V
present
across control
MV terminals after
ignitor warm-
up time?
Replace control.
Check operation.
NO
YES
NO
Purge system of
air. Energize
system. Check
operation.
Adjust manifold
to required
pressure setting.
Check operation.
Restore gas
supply at source.
Check operation.
Replace ignitor.
Check operation.
Replace broken or
defective wiring.
Check operation.
NO NO
YES
Is outlet
pressure
detected after
ignitor warm-
up time?
YES
Is gas at
source?
Is 120V
present at
ignitor leads?
4D
4J
Is manifold
pressure
adjusted to
required
setting?
YES
NO
Turn manual knob
to ON position.
Check operation.
NO
Refer to service
facts or installer’s
guide for proper
pressure settings.
Connect voltmeter
to gas valve
leads. Energize
system.
WARNING
!
TROUBLESHOOTING
GUIDE
INTEGRATED FURNACE
CONTROL MODULE
CHART 4
www.white-rodgers.com
If diagnostic indicator (LED)
shows continuous flashing, turn
off gas supply at source before
disconnecting electrical power!
TECHNICAL HELP
263
Page 6
Flame
Sensor
Check
Does main
burner remain
lit?
YES NO
YESNO
Is blower
at heat speed
within 1 minute
of burner ignition?
Does ignitor remain
energized with
flame present?
De-energize system.
Disconnect 12-pin
connector. Connect
ohmmeter from flame
sensor pin FP to
burner GROUND.
Replace sensor.
Energize system.
Check operation.
NO
Replace control.
Check operation.
YES
5A 5C5B
5E
5G
Disconnect flame
sensor from wire.
Measure continuity from
wire end to FP pin
on 12-pin connector.
5I
Disconnect AC power to
system at main fuse or
circuit breaker. Connect
voltmeter from control
terminal LINE NEUTRAL
to BURNER GROUND.
Energize module.
5L
NO
NO
Is 120V
present at
control terminals
HEAT & CIR
NEUTRAL?
5D
5K
5O
5H
YES
YES
Is resistance
less than
50 megohms?
Is 1 microamp
or more
present?
Replace flame
sensor lead. Check
operation.
NO
YES
NO
Replace control
module. Check
operation.
Clean surface of
flame sensor with
fine steel wool.
Reinstall. Check
operation.
Reverse 120V
LINE & NEUTRAL
wires. Energize
system. Check
operation.
Repair or
replace wire.
Energize system.
Check operation.
Connect ground
wire from burner to
12-pin connector
terminal GROUND.
Check operation.
NO
YES
YES
YES
Is
control
ground wire
connected to
burner
ground?
5J
NO NO
Is sensor
lead good?
Disconnect lead
from flame sensor.
Connect ohmmeter
from sensor to
burner ground.
5N
Connect a microammeter
in series with flame
sensor and sensor
lead. Energize system.
Measure current when
burner ignites.
5F
Is resistance
less than
50 megohms
(50,000,000
Ohms)?
5M
Is 120V
present at
burner ground?
NO
5P
Remove
sensor.
Does sensor
have carbon or
dust buildup?
YES
Repair wiring
and/or replace
indoor blower
motor. Check
operation.
System is
functioning
properly.
YES
WARNING
!
INTEGRATED FURNACE
CONTROL MODULE
CHART 5
TROUBLESHOOTING
GUIDE
TECHNICAL HELP
264
If diagnostic indicator (LED)
shows continuous flashing, turn
off gas supply at source before
disconnecting electrical power!
www.white-rodgers.com
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