Lenox ML180UHE, Lennox Merit Series Gas Furnace Upflow/Horizontal air discharge Heating Sequence

Troubleshooting: Heating Sequence of Operation (Continued)

HEATING SEQUENCE CONTINUED

NORMAL HEATING MODE

ABNORMAL HEATING MODE

15-SECOND COMBUSTION AIR INDUCER PREPURGE

INITIATED BY CLOSED PRESSURE SWITCH.

LED FLASHES CODE 13 −

YES

NO

LOW LINE VOLTAGE.

NO

IGNITOR WARM-UP −− 20 SECONDS.

IS VOLTAGE ABOVE 70 VOLTS?

ONCE VOLTAGE IS ABOVE

YES

75 VOLTS, HEATING

YES

SEQUENCE RESTARTS.

4-SECOND TRIAL FOR IGNITION.

GAS VALVE OPENS. IGNITOR ENERGIZED FOR

FIRST 3 SECONDS OF THE TRIAL.

GAS VALVE OFF. COMBUSTION AIR INDUCER ON.

INDOOR BLOWER OFF.

NO

YES

NO

HAS CONTROL FAILED TO SENSE FLAME FOR

FIVE CONSECUTIVE TRIES DURING A SINGLE

FLAME STABILIZATION PERIOD.

HEAT DEMAND?

4 SECONDS

YES

FLAME RECTIFICATION CURRENT

LED SIGNAL WATCHGUARD FAILURE CODE

CHECK. CAN FLAME BE PROVEN WITHIN

WATCHGUARD MODE. GAS VALVE OFF.

4 SECONDS AFTER GAS VALVE OPENS?

COMBUSTION AIR INDUCER OFF.

(0.5 microamps)

INDOOR BLOWER OFF WITH DELAY

YES

NO

IS 60-MINUTE RESET PERIOD COMPLETE?

YES

NO

FLAME PRESENT?

HAS CONTROL RESET IGNITION

SEQUENCE FOUR TIMES?

YES

YES

LED FLASHES CODE

NO

LED FLASHES CODE 4 − LOW FLAME

7 − PRIMARY LIMIT

OPEN. GAS VALVE,

FLAME SIGNAL 1.5 MICROAMPS OR GREATER?

SIGNAL.

COMB. AIR INDUCER

(Does not affect operation of control)

YES

AND INDOOR BLOW-

ER OFF. LEDs SIG-

INDOOR BLOWER ON

NAL LIMIT SWITCH

AFTER 30−SECOND DELAY

LED FLASHES CODE 7 − PRIMARY LIMIT OPEN

OPEN UNTIL MAIN

YES

POWER IS

GAS VALVE DE−ENERGIZED.

INTERRUPTED OR

NO

COMBUSTION AIR INDUCER DE−ENERGIZED.

T’STAT IS CYCLED

PRIMARY LIMIT SWITCH CLOSED?

INDOOR BLOWER ON UNTIL SWITCH CLOSES.

OFF/ON FOR 1 SEC.

LIMIT SWITCH CLOSED?

YES

MINIMUM. 60−MINUTE

WATCHGUARD PE-

YES

RIOD STARTS AT

HAS PRIMARY LIMIT RESET

TIME LIMIT CLOSES.

YES

TIME EXCEEDED 3 MINUTES?

IS 60−MIN. PERIOD

NO

COMPLETE?

NO

LED FLASHES CODE 8 − ROLLOT SWITCH OPEN.

ROLLOUT SWITCH CLOSED?

GAS VALVE POWER OFF. COMBUSTION AIR INDUCER POWER

YES

ON. INDOOR BLOWER ON SEQUENCE HOLDS UNTIL ROLLOUT

SWITCH IS RESET AND MAIN POWER IS INTERRUPTED OR

NO

THERMOSTAT IS CYCLED OFF/ON FOR 1 SEC. MINIMUM.

COMBUSTION AIR PRESSURE

SWITCH CLOSED?

YES

THERMOSTAT DEMAND SATISFIED.

YES

LED SLOW FLASH.

YES

COMB. AIR INDUCER CONTINUES 5-SECOND

POST PURGE AFTER T’STAT DEMAND IS SATISFIED. INDOOR AIR BLOWER COMPLETES SELECTED

DELAY BEFORE SHUTTING OFF.

HAS PRESSURE SWITCH OPENED 5 TIMES			LED FLASHES
IN THE SAME HEAT DEMAND?
			CODE 10
NO	YES		1 HR PRESSURE
GAS VALVE DE−ENERGIZED. COMBUSTION AIR			SWITCH
			WATCHGUARD
INDUCER ON. INDOOR BLOWER OFF WITH
			MODE
DELAY. HAS CAB PRESSURE SWITCH CLOSED
WITHIN 2.5 MINUTES?
		YES
NO
5-MINUTE PRESSURE SWITCH
WATCHGUARD MODE.

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