Lennox ML195UH Installation Instructions Manual page 51

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
FIRST 3 SECONDS OF THE TRIAL.
YES
FLAME STABILIZATION PERIOD.
4 SECONDS
FLAME RECTIFICATION CURRENT
CHECK. CAN FLAME BE PROVEN WITHIN
4 SECONDS AFTER GAS VALVE OPENS?
(0.5 microamps)
YES
FLAME PRESENT?
YES
FLAME SIGNAL 1.5 MICROAMPS OR GREATER?
YES
INDOOR BLOWER ON
AFTER 30−SECOND DELAY
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 INDUCER CONTINUES 5-SECOND
POST PURGE AFTER T'STAT DEMAND IS SATISFIED.
INDOOR AIR BLOWER COMPLETES SELECTED OFF"
DELAY BEFORE SHUTTING OFF.
HEATING SEQUENCE CONTINUED
NO
IS VOLTAGE ABOVE 90 VOLTS?
GAS VALVE OFF. COMBUSTION AIR INDUCER 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 INDUCER DE−ENERGIZED.
INDOOR BLOWER ON UNTIL SWITCH CLOSES.
NO
LED #1 −− SLOW FLASH. LED #2 −− ON.
NO
NO
HAS CAB SWITCH CLOSED IN 2.5 MINUTES?
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ABNORMAL HEATING MODE
YES
INDOOR BLOWER OFF.
HEAT DEMAND?
WATCHGUARD MODE. GAS VALVE OFF.
COMBUSTION AIR INDUCER 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 / SECONDARY
LIMIT RESET TIME
EXCEEDED 3 MINUTES?
GAS VALVE POWER OFF.
COMBUSTION AIR INDUCER POWER ON.
INDOOR BLOWER ON
LED #1 −− ON. LED #2 −− SLOW FLASH.
SEQUENCE HOLDS UNTIL ROLLOUT SWITCH IS RESET
AND MAIN POWER IS INTERRUPTED OR
THERMOSTAT IS CYCLED OFF/ON FOR 1 SEC. MINIMUM.
HAS PRESSURE SWITCH OPENED 5
TIMES IN THE SAME HEAT DEMAND?
NO
GAS VALVE DE−ENERGIZED.
COMBUSTION AIR INDUCER ON.
INDOOR BLOWER OFF WITH DELAY
LED #1 −− OFF. LED #2 −− SLOW FLASH.
NO
5-MINUTE PRESSURE SWITCH
WATCHGUARD MODE.
LEDS SIGNAL
ALTERNATING
NO
FAST FLASH UNTIL
VOLTAGE IS ABOVE
95 VOLTS, THEN
RESTARTS HEATING
SEQUENCE.
NO
YES
YES
NO
YES
LIMIT SWITCH WATCHGUARD
MODE. GAS VALVE, COMB. AIR
INDUCER AND INDOOR BLOW-
ER OFF. LEDs SIGNAL LIMIT
SWITCH OPEN UNTIL MAIN
POWER IS
INTERRUPTED OR
T'STAT IS CYCLED
OFF/ON FOR 1 SEC.
MINIMUM. 60−MINUTE
WATCHGUARD PE-
RIOD STARTS AT
TIME LIMIT CLOSES.
IS 60−MIN. PERIOD
YES
COMPLETE?
NO
1 HR
PRESSURE
SWITCH
YES
WATCHGUARD
MODE