Lennox 80MGF Series Manual page 37

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
1 SECOND AFTER VALVE OPENS.
NO FLAME SENSED DURING THIS PERIOD.
BOARD 97L48 ONLY: IGNITOR ENERGIZED FOR THE
FULL 4−SECOND TRIAL FOR IGNITION.
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 0.7 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 INDUCER CONTINUES 5-SECOND POST PURGE
AFTER T'STAT DEMAND IS SATISFIED. INDOOR AIR BLOWER
COMPLETES SELECTED OFF" DELAY BEFORE SHUTTING OFF.
ACB.HEAT SPEED, HTG ACC TERM. AND ACC TERM. 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.
NO HAS CONTROL FAILED TO SENSE FLAME FOR
FIVE CONSECUTIVE TRIES DURING A SINGLE
IGNITION WATCHGUARD MODE. GAS VALVE OFF.
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF WITH DELAY
LED 1 ALT. SLOW FLASH LED 2 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)
LED #1 −− SLOW FLASH
LED #2 −− FAST FLASH
GAS VALVE DE−ENERGIZED.
COMBUSTION AIR INDUCER
DE−ENERGIZED.INDOOR BLOWER
NO
ON UNTIL SWITCH CLOSES.LED #1
−− SLOW FLASH. LED #2 −− ON.
IS LIMIT SWITCH CLOSED?
YES
HAS PRIMARY/SECONDARY LIMIT RESET.
(See table 9 DIAGNOSTIC CODES for limit reset operation)
NO
COMBUSTION AIR INDUCER POWER OFF.
LED #1 −− ON. LED #2 −− SLOW FLASH.
SEQUENCE HOLDS UNTIL ROLLOUT SWITCH IS RESET
NO
GAS VALVE DE−ENERGIZED.
COMBUSTION AIR INDUCER ON.
INDOOR BLOWER OFF WITH DELAY
LED #1 −− OFF. LED #2 −− SLOW FLASH.
HAS CAB SWITCH CLOSED IN 2.5 MINUTES?
Page 37
NO
NO
INDOOR BLOWER OFF.
HEAT DEMAND?
LIMIT SWITCH WATCH GUARD
MODE. GAS VALVE OFF.
COMB. AIR INDUCER OFF. IN-
DOOR BLOWER OFF WITH
DELAY. LED#1−SLOW FLASH
LED#2− ON. IS 60MINUTE RE-
SET PERIOD COMPLETE.?
GAS VALVE POWER OFF.
INDOOR BLOWER OFF WITH DELAY
NO
5-MINUTE PRESSURE SWITCH
WATCHGUARD MODE.
LEDS SIGNAL
ALTERNATING
FAST FLASH
NO
NO
YES
YES
NO
YES
NO
YES
YES
YES