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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 filter dirty or plugged?
• Is the flame 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
17
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 verified, check the Blower Limit Switch and
reset if necessary. See
• If the furnace operates when the Blower Limit Switch is
reset, contact a qualified service technician to identify
and repair the problem.
• If the furnace still doesn't operate, check the Flame
Roll-out Switches
(Figure
• If the furnace operates when the Flame Rollout Switch
is reset, contact a qualified service technician to identify
and repair the problem.
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
replaced, use only factory authorized replacement parts specified in the Replacement Parts List provided online.
Blower Limit Switch - Prevents 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 - Verifies when a flame has carried over from the igniter to the opposite end burner. If no flame is
detected, the furnace will shut down within 4 seconds.
Flame Roll-Out Switch - Verifies that the burner flames are drawn into the heat exchanger tubes. If the burner
flames are not properly drawn into the heat exchanger, the flame roll-out switch will close the gas valve and initiate
the shutdown cycle.
Gas Valve - Controls the flow of gas to the burners. When the gas valve is energized it automatically opens and
regulates the gas pressure in the manifold.
Inducer Assembly - Vents products of combustion to the outside.
Pressure Switches - Verifies that the inducer is drawing the combustion gases through the heat exchanger. The
pressure switch prevents furnace operation with excessive flue / condensate blockage or improper inducer operation.
Supply Air Limit Switch - Prevents the air temperature leaving the furnace from exceeding the maximum allowable
outlet air temperature.
Table 16
&
Table
Figure 40 (page 50).
40) and reset if necessary.
FURNACE COMPONENTS
Diagnostic Description
Control Fault (No Power)
L1/Neutral Polarity Fault
1 Hour Lockout
Normal Operation
Pressure Switch Closed Fault
Pressure Switch Open Fault
Open Limit Switch Fault
Motor Fault
Diagnostic Description
Low Flame Sensor Signal
Flame Present
Table 16. Furnace Control Board Fault Conditions
Diagnostic
Description
Control Fault (No Power)
Normal Operation
Fixed
Motor Fault
Speed
Furnaces
Twin Fault (no motor fault)
Communications Fault
Control Fault (No Power)
Variable
Normal Operation
Speed
Motor Fault
Furnaces
Communications Fault
Table 17. Motor Control Board Fault Conditions
Figure
40. If any component of the furnace must be
Green LED
Red LED
Off
Off
Flash
Flash
Alternating Flash
On
On
On
Flash
Flash
On
Flash
Off
On
Off
Yellow LED
Continuous Flash
On
Green
Red
LED
LED
Off
Off
On
On
On
Flash
Flash
On
Flash
Flash
Off
Off
On
On
On
Flash
Flash
Flash
49
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