Lennox G51MP SERIES Installation Instructions Manual page 50

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SureLight Troubleshooting: Heating Sequence of Operation (Continued)
NORMAL HEATING MODE
15-SECOND COMBUSTION AIR INDUCER PREPURGE
INITIATED BY CLOSED PRESSURE SWITCH.
YES
IGNITOR WARM-UP −− 20 SECONDS.
YES
4-SECOND TRIAL FOR IGNITION.
GAS VALVE OPENS. IGNITOR ENERGIZED FOR
UP TO 4 SECONDS.
YES
FLAME STABILIZATION PERIOD.
4 SECONDS
FLAME RECTIFICATION CURRENT
CHECK. CAN FLAME BE PROVEN WITHIN
4 SECONDS AFTER GAS VALVE OPENS?
(u0.24 microamps)
YES
FLAME PRESENT?
YES
FLAME SIGNAL ABOVE 0.34 MICROAMPS?
YES
INDOOR BLOWER ON DELAY BEGINS
(45 seconds.)
YES
PRIMARY AND SECONDARY LIMIT
SWITCHES CLOSED?
COMBUSTION AIR INDUCER
AUXILIARY LIMIT SWITCH CLOSED?
YES
ROLLOUT SWITCHES CLOSED?
YES
COMBUSTION AIR PRESSURE
SWITCH CLOSED?
YES
THERMOSTAT DEMAND SATISFIED.
YES
DS1 & DS2 SIMULTANEOUS SLOW FLASHES.
YES
COMB. AIR INDUCER CONTINUES 5-SECOND
POST PURGE AFTER T'STAT DEMAND IS SATISFIED.
INDOOR AIR BLOWER COMPLETES SELECTED OFF"
DELAY BEFORE SHUTTING OFF.
ABNORMAL HEATING MODE
IS VOLTAGE ABOVE 75 VOLTS?
NO
YES
IS THERE A PROPER GROUND?
YES
YES
IS IGNITOR INTACT AND CONNECTED?
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.
INDOOR BLOWER OFF.
NO
HAS CONTROL FAILED TO SENSE FLAME FOR
FIVE CONSECUTIVE TRIES DURING A SINGLE
HEAT DEMAND?
IGNITION WATCHGUARD MODE. GAS VALVE OFF.
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF WITH DELAY
DS1 ALT. SLOW FLASH DS2 ALT. SLOW FLASH
IS 60-MINUTE RESET PERIOD COMPLETE?
NO
HAS CONTROL RESET IGNITION
SEQUENCE FOUR TIMES?
LOW FLAME SIGNAL
NO
(Does not affect operation of control)
DS1 −− SLOW FLASH
DS2 −− FAST FLASH
GAS VALVE DE−ENERGIZED.
COMBUSTION AIR INDUCER
DE−ENERGIZED.INDOOR BLOWER
NO
ON UNTIL SWITCHES CLOSE. DS1
−− SLOW FLASH. DS2 −− ON.
IS LIMIT SWITCH CLOSED?
YES
HAVE PRIMARY/SECONDARY/CAI
AUX. LIMITS RESET (CLOSED)
WITHIN 3 MINUTES?
GAS VALVE POWER OFF.
NO
COMBUSTION AIR INDUCER POWER ON.
INDOOR BLOWER ON WITH DELAY
DS1 −− ON. DS2 −− SLOW FLASH.
SEQUENCE HOLDS UNTIL ROLLOUT SWITCH AND
THERMOSTAT IS RESET.
NO
GAS VALVE DE−ENERGIZED.
COMBUSTION AIR INDUCER ON.
INDOOR BLOWER OFF WITH DELAY
DS1 −− OFF. DS2 −− SLOW FLASH.
HAS CAB SWITCH CLOSED IN 2.5 MINUTES?
NO
5-MINUTE PRESSURE SWITCH
WATCHGUARD MODE.
Page 50
NO
DS1 & DS2
NO
SIGNAL
ALTERNATING
NO
FAST FLASH.
NO
YES
YES
NO
YES
LIMIT SWITCH WATCH-
GUARD MODE. GAS
VALVE OFF. COMB. AIR
INDUCER OFF. INDOOR
BLOWER OFF WITH
DELAY. DS1 − SLOW
FLASH DS2 − ON. IS
60MINUTE RESET
PERIOD COMPLETE?
NO
YES
YES
YES
YES