Lennox G27M Series Unit Information

3DJH 
HEATING SEQUENCE CONTINUED
NORMAL HEATING MODE ABNORMAL HEATING MODE
INDOOR BLOWER ON
ACB HEAT SPEED?
TWO--STAGE MODE
SINGLE STAGE TSTAT
PRESSURE SWITCH CLOSED?
TWO--STAGE MODE
CALL FOR 1st STAGE HEAT
CALL FOR 2nd STAGE
HEAT (HIGH FIRE)
FROM THERMOSTAT
2nd STAGE ON DELAY
ON CONTROL BOARD
COMPLETE.
TWO--STAGE MODE
SINGLE STAGE TSTAT
SINGLE--STAGE MODE
HIGH HEAT ONLY
TWO--STAGE MODE
CALL FOR 1st STAGE HEAT
CONTROL CHECKS: FLAME PRESENCE, CLOSED
PRIMARY & SECONDARY LIMITS, CLOSED PRESSURE
SWITCHES, CONTINUOUSLY CLOSED ROLLOUT
SWITCHES (during heating cycle).
SEE PREVIOUS SEQUENCES FOR FAILURE MODES.
GAS VALVE DE--ENERGIZED.
COMBUSTION AIR BLOWER POST--PURGE ---- 5 SECONDS.
(C.A.B DE--ENERGIZES HTG ACC TERMINAL DE--ENERGIZES)
INDOOR BLOWER
SELECTED TIME OFF DELAY.
YES
HIGH FIRE PRESSURE SWITCH CLOSED?
HIGH FIRE GAS VALVE OPEN?
GAS VALVE DE--ENERGIZED.
INDOOR BLOWER DE--ENERGIZED.
COMBUSTION AIR BLOWER ON FOR 2.5 MINUTES.
NO
NO
PRESSURE SWITCH
CLOSED?
PRESSURE SWITCH WATCHGUARD
COMBUSTION AIR BLOWER
DE--ENERGIZED.
5--MINUTE DELAY
COMBUSTION AIR
BLOWER ON.
PREPURGE
(See top of previous page.)
DEMAND FOR HEAT SATISFIED.
THERMOSTAT OPENS.
DIAGNOSTIC CODES
LED #1 LED #2 DESCRIPTION
SLOW FLASH
SLOW FLASH
SLOW FLASH
SLOW FLASH
FAST FLASH
FAST FLASH
ON
ON
OFF
ON
OFF
ON
SLOW FLASH
SLOW FLASH
SLOW FLASH
SLOW FLASH
FAST FLASH
FAST FLASH
ALTERNATE FLASH
Primary or secondary limit open
Rollout switch open
Flame sensed without gas valve energized
Pressure switch open
Power on
Heating demand
Polarity reversed
Low flame signal
Circuit board failure
Watchguard ---- burners failed to ignite
. 2.5
MINUTES
IGNITION CONTROL MAIN POWER ON.
CONTROL SELF DIAGNOSTIC CHECK.
IS CONTROL OPERATING NORMALLY?
YES
SIGNAL POLARITY REVERSED.
POWER ON
GAS VALVE OFF. COMBUSTION AIR BLOWER OFF.
INDOOR BLOWER OFF WITH NORMAL DELAY.
SIGNAL CIRCUIT BOARD FAILURE AT LED.
INTERRUPT MAIN POWER TO RESET CONTROL.
YES
TURN INDUCER ON FOR 1 SECOND.
IS POLARITY REVERSED?
NO
NO
IS THERE PROPER GROUND?
IS VOLTAGE
ABOVE 75 VOLITS
NO YES
NO
YES
COOLING SEQUENCE OF O PERATION
LOW VOLTAGE SIGNAL AT LED HOLDS
UNTIL VOLTAGE RISES ABOVE 75 VOLTS
SIGNAL IMPROPER
GROUND AT LED.
SIGNAL HOLDS
UNTIL UNIT IS
PROPERLY
GROUNDED.

Lennox G27M Series Specifications

General

Brand	Lennox
Model	G27M Series
Category	Furnace
Language	English