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Page 45
Troubleshooting: Heating Sequence of Operation (Continued)
HEATING SEQUENCE OF OPERATION
FIRST−STAGE (LOW FIRE) PRESSURE
SWITCH CLOSED WITHIN 2.0 MINUTES?
GAS VALVE OFF. COMBUSTION AIR INDUCER
OFF. INDOOR BLOWER OFF. UNIT WILL RETRY
AFTER 5−MINUTE WAIT PERIOD.
STATUS ERROR CODE 2 + 3.
YES
NO
15−SECOND COMBUSTION AIR INDUCER
PRE−PURGE INITIATED BY CLOSED FIRST−STAGE
PRESSURE SWITCH (or 15 SECOND
INTER−PURGE PERIOD.)
STATUS LED −− HEARTBEAT.
IGNITOR WARM−UP (20 SECONDS)
STATUS LED −− HEARTBEAT.
IS VOLTAGE ABOVE 90 VOLTS?
NO
COMBUSTION AIR INDUCER OFF, IGNITOR OFF.
SIGNAL HOLDS UNTIL VOLTAGE RISES ABOVE 95
VOLTS. STATUS ERROR CODE 4 + 8.
YES
NO
COMBUSTION AIR INDUCER OFF, IGNITOR OFF.
SIGNAL HOLDS UNTIL IGNITOR IS REPLACED
OR RECONNECTED.
STATUS ERROR CODE 4 + 7.
YES
AT END OF IGNITOR 20 SECOND WARM UP
PERIOD, 4−SECOND TRIAL FOR IGNITION.
GAS VALVE OPENS, IGNITOR ENERGIZED DURING
4−SECOND TRIAL UNTIL FLAME SENSED.
YES
4−SECOND FLAME STABILIZATION PERIOD.
FLAME RECTIFICATION CURRENT CHECK
CAN FLAME BE PROVEN WITHIN 4
SECONDS AFTER GAS VALVE OPENS?
(u0.20 microamps)
GAS VALVE OFF. COMBUSTION AIR
INDUCER ON. INDOOR BLOWER OFF.
STATUS LED −− HEARTBEAT.
HAS CONTROL FAILED TO SENSE
FLAME FOR FIVE CONSECUTIVE TRIES
DURING A SINGLE HEAT DEMAND?
YES
THERMOSTAT CALLS FOR HEAT
STATUS LED − HEARTBEAT.
(Refer to box A on previous page)
YES
FLAME PRESENT?
NO
HAS CONTROL RESET IGNITION SEQUENCE
FOUR (4) TIMES?
WATCHGUARD MODE.
STATUS ERROR CODE 4 + 3.
YES
CONTINUED ON NEXT PAGE
YES
NO
NO
CONTINUED
IS IGNITOR INTACT AND CONNECTED?
WATCHGUARD MODE. GAS VALVE OFF,
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF.
STATUS ERROR CODE 4 + 1.
IS 60−MINUTE RESET PERIOD COMPLETE?
NO
YES
1
1
1
If the furnace is operating on continuous fan mode (terminals R" and G" are energized), the combustion
air inducer will energize on high speed, the gas valve will energize on second−stage heat and the furnace
will operate on high fire. Furnace will stay on high fire 60 seconds then switch to low fire.
2
2
If combustion air inducer is operating on high speed and gas valve is energized on second−
stage heat, 20 seconds after flame is sensed furnace will switch to low fire.
COMBUSTION AIR INDUCER
ENERGIZED ON HIGH SPEED
LOW AND HIGH
PRESSURE SWITCH
CLOSED WITHIN 30
SECONDS
YES
NO