Lennox
G60UHX Series, Service Manual

Page: 28 / 40

Page 28
HEATING SEQUENCE OF OPERATION
NORMAL AND ABNORMAL HEATING MODE
CONTROL SELF−CHECK OKAY?
YES
GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF. (RESET CONTROL BY
TURNING MAIN POWER OFF.) DS1 ON, DS2 ON
NO
POLARITY REVERSED.
DS1 −− FAST FLASH
DS2 −− SLOW FLASH
POWER ON
POLARITY OKAY?
NO
SIGNAL HOLDS UNTIL UNIT IS PROPERLY GROUNDED.
DS1 AND DS2 ALTERNATING FAST FLASH.
IS THERE A
PROPER GROUND?
IS VOLTAGE
ABOVE 75 VOLTS?
SIGNAL HOLDS UNTIL VOLTAGE RISES ABOVE 75 VOLTS.
DS1 AND DS2 ALTERNATING FAST FLASH.
NO
YES
NO
YES
GAS VALVE OFF. COMBUSTION AIR INDUCER
OFF. INDOOR BLOWER OFF. CHECK FOR
BROKEN IGNITOR OR OPEN IGNITER CIRCUIT.
DS1 AND DS2 ALTERNATING FAST FLASH.
BURNER OFF?
(CONTINUOUS FLAME CHECK)
YES
NO
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.
INDOOR BLOWER ON HEATING SPEED.
DS1 SLOW FLASH, DS2 OFF.
A
NORMAL OPERATION:
DS 1 −− SIMULTANEOUS SLOW FLASH
DS 2 −− SIMULTANEOUS SLOW FLASH
B
THERMOSTAT CALLS FOR HEAT:
DS 1 −− SIMULTANEOUS FAST FLASH
DS 2 −− SIMULTANEOUS FAST FLASH
YES
PRIMARY AND SECONDARY LIMIT
SWITCHES CLOSED?
YES
NO
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER ON. HAS PRIMARY OR
SECONDARY LIMIT RESET WITHIN 3 MINUTES?
DS1 SLOW FLASH, DS2 ON.
ROLLOUT SWITCH CLOSED?
GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
HAS MANUAL ROLLOUT SWITCH(ES) BEEN
RESET (CLOSED) WITHIN 3 MINUTES?
DS1 SLOW FLASH, DS2 ON.
NO
YES
FIRST (LOW) STAGE PRESSURE SWITCH
CONTACTS OPEN?
NO
GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF. CONTROL REMAINS UNTIL
PRESSURE SWITCH IS DETECTED OPEN.
DS1 OFF, DS2 SLOW FLASH.
YES
GAS VALVE OFF.
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF.
CONTROL WILL NOT ATTEMPT SECOND−STAGE
OPERATION DURING THIS HEAT DEMAND.
FIRST−STAGE OPERATION WILL BE ATTEMPTED.
DS1 OFF, DS2 FAST FLASH.
NO
TWO−STAGE OR SINGLE−STAGE THERMOSTAT
CALL FOR HEAT
COMBUSTION AIR INDUCER ON LOW SPEED.
DS1 AND DS2 SIMULTANEOUS FAST FLASH
CONTINUED ON NEXT PAGE
NO
NO
60−MINUTE LIMIT WATCHGUARD MODE.
GAS VALVE OFF, COMBUSTION AIR INDUCER
OFF, INDOOR BLOWER OFF WITH DELAY.
DS1 AND DS2 ALTERNATING SLOW FLASH.
YES
NO
YES
SECOND (HIGH) STAGE PRESSURE SWITCH
CONTACTS OPEN?
Slow flash rate equals 1Hz (one flash per second). Fast flash rate equals 3 Hz (three flashes per second).