27
Table 4. Motor Control Board Fault Conditions
Diagnostic
Description
Green
LED
Red
LED
Fixed
Speed
Furnaces
Control Fault (No Power)
Off
Off
Normal Operation
On
On
Motor Fault
On
Flash
Twin Fault (no motor fault)
Flash
On
Communications Fault
Flash
Flash
Variable
Speed
Furnaces
Control Fault (No Power)
Off
Off
Normal Operation
On
On
Motor Fault
On
Flash
Communications Fault
Flash
Flash
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!)
• Are all the LED’s on the furnace and motor control
boards constantly ON? If not, refer to Tables 3 - 4 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
(Figure 28, page 41) and reset if necessary.
• 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 Flame
Roll-out Switches (Figure 28) and reset if necessary.
• If the furnace operates when the Flame 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 3. Furnace Control Board Fault Conditions
