Lennox F8AUH series Service Manual page 21

NORMAL HEATING MODE
15-SECOND COMBUSTION AIR BLOWER PREPURGE
INITIATED BY CLOSED PRESSURE SWITCH.
YES
IGNITOR WARM-UP −− 11 TO 21 SECONDS.
YES
4-SECOND TRIAL FOR IGNITION.
GAS VALVE OPENS. IGNITOR ENERGIZED FOR
1 SECOND AFTER VALVE OPENS.
NO FLAME SENSED DURING THIS PERIOD.
YES
FLAME STABILIZATION PERIOD.
4 SECONDS
FLAME RECTIFICATION CURRENT
CHECK. CAN FLAME BE PROVEN WITHIN
4 SECONDS AFTER GAS VALVE OPENS?
(u0.15 microamps)
YES
FLAME PRESENT?
YES
FLAME SIGNAL ABOVE 0.2 MICROAMPS?
YES
INDOOR BLOWER ON DELAY BEGINS
(45 seconds.)
YES
PRIMARY AND SECONDARY LIMIT
SWITCHES CLOSED?
YES
ROLLOUT SWITCH
CLOSED?
YES
COMBUSTION AIR PRESSURE
SWITCH CLOSED?
YES
THERMOSTAT DEMAND SATISFIED.
YES
LED #1 & #2 SIMULTANEOUS SLOW FLASHES.
YES
COMB. AIR BLOWER CONTINUES 5-SECOND
POST PURGE AFTER T'STAT DEMAND IS SATISFIED.
INDOOR AIR BLOWER COMPLETES SELECTED OFF"
DELAY BEFORE SHUTTING OFF.
HEATING SEQUENCE CONTINUED
ABNORMAL HEATING MODE
NO
IS THERE A PROPER GROUND?
GAS VALVE OFF. COMBUSTION AIR BLOWER ON.
NO
HAS CONTROL FAILED TO SENSE FLAME FOR
FIVE CONSECUTIVE TRIES DURING A SINGLE
LEDs SIGNAL WATCHGUARD FAILURE CODE.
NO
NO
(Does not affect operation of control)
COMBUSTION AIR BLOWER DE−ENERGIZED.
INDOOR BLOWER ON UNTIL SWITCH CLOSES.
NO
LED #1 −− SLOW FLASH. LED #2 −− ON.
NO
NO
LED #1 −− OFF. LED #2 −− SLOW FLASH.
HAS CAB SWITCH CLOSED IN 2.5 MINUTES?
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YES
INDOOR BLOWER OFF.
HEAT DEMAND?
WATCHGUARD MODE. GAS VALVE OFF.
COMBUSTION AIR BLOWER OFF.
INDOOR BLOWER OFF WITH DELAY
IS 60-MINUTE RESET PERIOD COMPLETE?
HAS CONTROL RESET IGNITION
SEQUENCE FOUR TIMES?
LOW FLAME SIGNAL
LED #1 −− SLOW FLASH
LED #2 −− FAST FLASH
GAS VALVE DE−ENERGIZED.
IS LIMIT SWITCH CLOSED?
YES
HAS PRIMARY LIMIT OPENED
FIVE TIMES DURING ONE
UNSATISFIED HEATING DEMAND?
GAS VALVE POWER OFF.
COMBUSTION AIR BLOWER POWER ON.
INDOOR BLOWER ON
LED #1 −− ON. LED #2 −− SLOW FLASH.
SEQUENCE HOLDS UNTIL ROLLOUT SWITCH IS RESET
AND MAIN POWER IS INTERUPTED OR
THERMOSTAT IS CYCLED OFF/ON FOR 1 TO 20 SEC.
GAS VALVE DE−ENERGIZED.
COMBUSTION AIR BLOWER ON.
INDOOR BLOWER OFF WITH DELAY
NO
5-MINUTE PRESSURE SWITCH
WATCHGUARD MODE.
NO
LEDS SIGNAL
ALTERNATING
FAST FLASH
NO
YES
YES
NO
YES
NO
YES