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TROUBLESHOOTING
If the furnace fails to operate check the following:
• Is the thermostat operating properly?
• Are the blower compartment door(s) in place?
• Is the furnace disconnect closed?
• Has the circuit breaker tripped or the control board fuse
burned open?
• Is the gas turned on?
• Are any manual reset switches open?
• Is the fi lter dirty or plugged?
• Is the fl ame sensor coated? Remove and clean with
steel wool.
(Do not use emery cloth or sandpaper!)
• Is there blockage in the condensate drain switch? Also
verify that there is no double trapping of condensate.
• Is the secondary heat exchanger free of debris and
clogs?
• I s eva p o ra t o r c o i l c l e a n a n d f r e e o f d e b r i s
(If applicable).
• Are all the LED’s on the furnace control board constantly
ON? If not, refer to Table 7 or the wiring diagram (Figure
40, page 39) to determine fault condition.
IMPORTANT NOTE: The furnace will lock out after 5
failed attempts for ignition and will try again every
hour if the call for heat remains.
• If the Inducer Blower is operating, and items above
have been verifi ed, check the blower limit switch and
reset if necessary. See Figure 45 or 46 (page 47) for
component location.
• If the furnace operates when the blower limit switch is
reset, contact a qualifi ed service technician to identify
and repair the problem.
• If the furnace still doesn’t operate, check the fl ame roll-
out switches (Figure 45 or 46) and reset if necessary.
• If the furnace operates when the fl ame rollout switch is
reset, contact a qualifi ed service technician to identify
and repair the problem.
Diagnostic Description
Green
LED
Red
LED
Control Fault (No Power)
Off
Off
L1/Neutral Polarity Fault
Flash
Flash
1 Hour Lockout
Alternating Flash
Normal Operation
On
On
Pressure Switch Closed Fault
On
Flash
Pressure Switch Open Fault
Flash
On
Open Limit Switch Fault
Flash
Off
Motor Fault
On
Off
Diagnostic Description
Yellow LED
Low Flame Sensor Signal
Continuous Flash
Flame Present
On
Table 7. Control Board Fault Codes
DESCRIPTION OF COMPONENTS
The descriptions below are various functional components
that affect the operation and shutting down of this furnace.
Some of these components and their locations are shown
in Figures 45 and 46 (page 47). If any component of the
furnace must be replaced, use only factory authorized
replacement parts specifi ed in the Replacement Parts
List provided online.
Blower Limit Switch
The Blower switch prevents furnace operation when blower
is not operational.
Condensate Drain Switch
The Condensate Drain Switch will shut down the furnace
if the condensate drain from the Collector Pan becomes
clogged.
Flame Sensor
The fl ame sensor verifi es when a fl ame has carried over
from the igniter to the opposite end burner. If no fl ame is
detected, the furnace will shut down within 4 seconds.
Flame Roll-Out Switch
The fl ame roll-out switch verifi es that the burner fl ames
are drawn into the heat exchanger tubes. If the burner
fl ames are not properly drawn into the heat exchanger, the
fl ame roll-out switch will close the gas valve and initiate
the shutdown cycle.
Gas Valve
The gas valve controls the fl ow of gas to the burners.
When the gas valve is energized it automatically opens
and regulates the gas pressure in the manifold.
Inducer Assembly
The inducer assembly vents products of combustion to
the outside
.
Pressure Switch
The pressure switch verifi es that the inducer is drawing
the combustion gases through the heat exchanger. If
the fl ame is not properly drawn into the heat exchanger
tube, the rollout switch or the fl ame sensor will shut the
furnace down.
Supply Air Limit Switch
The supply air limit switch prevents the air temperature
leaving the furnace from exceeding the maximum allowable
outlet air temperature.
