Lennox
G60UHX Series, Service Manual

Page: 31 / 40

Page 31
HEATING SEQUENCE OF OPERATION
IS PRIMARY AND SECONDARY LIMIT
AND ROLLOUT SWITCH CLOSED?
NO
GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER ON.
DS1 SLOW FLASH, DS2 ON.
HAS PRIMARY, SECONDARY OR ROLLOUT
SWITCH CLOSED WITHIN 3 MINUTES?
NO
LIMIT SWITCH WATCHGUARD MODE. GAS VALVE
OFF. COMBUSTION AIR INDUCER OFF. INDOOR
BLOWER OFF WITH DELAY. IS 60−MINUTE RESET
PERIOD COMPLETE? DS SLOW FLASH, DS2 ON.
SEE BOX B
THERMOSTAT CALLS FOR HEAT
DS 1 AND DS 2 SIMULTANEOUS FAST FLASH
YES
FIRST−STAGE (LOW FIRE) HEAT
PRESSURE SWITCH CLOSED?
NO
SEE BOX A
NORMAL OPERATION
DS1 AND DS2 SIMULTANEOUS SLOW FLASH.
YES
YES
GAS VALVE OFF, COMBUSTION AIR INDUCER OFF
AFTER 15 SECOND POST PURGE, INDOOR
BLOWER OFF AFTER DELAY.
DS1 OFF, DS2 FAST FLASH.
RETURN TO HEAT DEMAND?
YES
YES
NO
RETURN TO FIRST−STAGE HEAT MODE.
FIRST−STAGE CONTINUES UNTIL SECOND−
STAGE PRESSURE SWITCH CAN BE PROVEN
or HEAT DEMAND IS SATISFIED. A FIVE (5)
MINUTE WAIT PERIOD IS INITIATED BEFORE
RETRY. WERE 5 ATTEMPTS MADE FOR
SECOND−STAGE HEAT?
YES
NO
SEE BOX C
FIRST−STAGE HEAT DEMAND SATISFIED?
HEAT DEMAND SATISFIED?
DS1 AND DS2 SIMULTANEOUS FAST FLASH.
YES
TWO STAGE THERMOSTAT MODE?
(E20 SET AT TWO")
SINGLE−STAGE THERMOSTAT MODE
(E20 SET AT SINGLE")
YES
YES
HEAT DEMAND SATISFIED?
DS1 AND DS2
SIMULTANEOUS FAST FLASH.
FIRST AND SECOND STAGE HEAT
DEMAND SATISFIED SIMULTANEOUSLY.
DS1 & DS2 SIMULTANEOUS FAST FLASH.
YES
YES
GAS VALVE OFF, COMBUSTION AIR
INDUCER OFF AFTER POST PURGE
PERIOD, INDOOR BLOWER OFF AF-
TER SELECTED DELAY.
DS1 AND DS2
SIMULTANEOUS FAST FLASH
DEMAND FOR HEAT SATISFIED.
POWER ON STAND BY.
DS1 AND DS2
SIMULTANEOUS SLOW FLASH
YES
SECOND STAGE HEAT
DEMAND SASTISFIED?
DS1 AND DS2
SIMULTANEOUS FAST FLASH.
NO
GAS VALVE, COMBUSTION AIR INDUCER
AND INDOOR BLOWER RETURN TO FIRST−
STAGE OPERATION.
DS1 AND DS2 SIMULTANEOUS FAST FLASH.
YES
FIRST STAGE HEAT DEMAND SATISFIED?
YES
GAS VALVE OFF. COMBUSTION AIR INDUCER
OFF AFTER 5−SECOND POST−PURGE PERIOD.
INDOOR BLOWER OFF. DELAY INITIATED.
DS1 & DS2 SIMULTANEOUS FAST FLASH.
CONTINUED
SECOND−STAGE (HIGH FIRE) HEAT
PRESSURE SWITCH CLOSED?