Lennox International Inc MERIT SERIES GAS FURNACE DOWNFLOW AIR DISCHARGE, ML193DF

Troubleshooting: Cooling Sequence of Operation

COOLING SEQUENCE OF OPERATION

NORMAL COOLING MODE						ABNORMAL COOLING MODE
		POWER ON
IGNITION CONTROL MAIN POWER ON.
				NO		GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
CONTROL SELF DIAGNOSTIC CHECK.						INDOOR BLOWER OFF WITH NORMAL DELAY.
IS CONTROL OPERATING NORMALLY?						SIGNAL CIRCUIT BOARD FAILURE AT LED.
		YES				INTERRUPT MAIN POWER TO RESET CONTROL.
				NO
						SIGNAL IMPROPER GROUND AT LED.
IS THERE A PROPER GROUND?						CONTROL WILL CONTINUE TO CALL FOR COOLING
		YES				IN THIS CONDITION.
				NO		SIGNAL POLARITY REVERSED AT LED. CONTROL
	IS POLARITY CORRECT?					WILL CONTINUE TO CALL FOR COOLING IN THIS
						CONDITION.
		YES
			NO
		IS VOLTAGE				LED SIGNALS LOW VOLTAGE. CONTROL WILL
		ABOVE 90 VOLTS?				CONTINUE TO CALL FOR COOLING
		YES				IN THIS CONDITION.
				GAS VALVE OFF. COMBUSTION AIR INDUCER ON.
				NO		INDOOR BLOWER ON.
ROLLOUT SWITCH MONITORED CONTINUOUSLY.						SIGNAL ROLL-OUT SWITCH OPEN AT LED.
IS ROLLOUT SWITCH CLOSED?						SEQUENCE HOLDS UNTIL ROLLOUT SWITCH CLOSES
					AND MAIN POWER IS INTERRUPTED OR THERMOSTAT
		YES				IS CYCLED OFF/ON FOR 1 SEC. MINIMUM.

LED: SLOW FLASH RATE REMAINS UNCHANGED

THROUGHOUT COOLING CYCLE.

THERMOSTAT CALLS FOR COOLING.

COMPRESSOR CONTACTOR AND SYSTEM FAN

ENERGIZED WITH 2-SECOND DELAY

(COOLING SPEED). EAC TERM. ENERGIZED.

THERMOSTAT OPENS.

COMPRESSOR OFF.

SYSTEM FAN AND EAC TERM. OFF

WITH 45-SECOND DELAY.

Page 47