Electrical Checkout - Lennox G21Q3-40 Unit Information

SET FOR HEAT DEMAND
CLOSE DOOR TO ACTUATE SWITCH.
IS 120VAC PRESENT AT TRANSFORMER PRIMARY?
NO
DOUBLE CHECK WIRING CONNECTIONS
AND DOOR INTERLOCK SWITCH.
IS UNIT FUSE BLOWN?
NO
REPLACE
TRANSFORMER.
PLACE
NO
DETERMINE CAUSE OF OPEN LIMIT
AND/OR REPLACE IF DEFECTIVE.

ELECTRICAL CHECKOUT

NOTE− Numbered steps refer to illustrations on page 61.
IS THERMOSTAT PROPERLY SET?
NO
CHECK FOR 120VAC POWER TO UNIT & ADEQUATE GROUNDING.
(GROUNDING REQUIRED FOR PROPER OPERATION OF IGNITION SYS
IS BLOWER DOOR CLOSED PROPERLY ON INTERLOCK SWITCH?
NO
NO
YES
YES TURN OFF POWER TO UNIT.
4
IS DIFFERENTIAL SWITCH CLOSED?
MAKE OHMMETER CHECK.
RE
NO
FUSE.
REPLACE SWITCH.
Page 59
SYSTEM MAY BE LOCKED OUT. TURN THERMOSTAT HEATING DEMAND
OFF AND ON AGAIN. NOTE CONTINUE THROUGH TROUBLESHOOTING
FLOW CHART TO LOCATE REASON FOR LOCKOUT.
TEM.)
YES
1
IS 24VAC PRESENT ACROSS TERMINAL
R & C ON LOW VOLTAGE STRIP?
2
NO
CHECKOUT & REPAIR
THERMOSTAT AND/OR WIRING.
1. CONNECT 24VAC METER ACROSS GAS VALVE TERMINAL.
2. BREAK & REMAKE THERMOSTAT DEMAND TO RESTART UNIT CYCLE.
3
3.AFTER 30 TO 35 SECONDS PRE−PURGE, IS 24VAC PRESENT AT GAS
VALVE TERMINALS FOR APPROXIMATELY 7 SECONDS?
NO
YES
ARE LIMITS CLOSED?
MAKE OHMMETER CHECK.
5
CHECK ALL WIRING CONNECTION
INTERNAL AND EXTERNAL TO UNIT. REPAIR
ANY LOOSE OR DAMAGED CONNECTIONS.
TURN ON POWER. SET THERMOSTAT FOR HEAT DEMAND.
IS 24VAC PRESENT ACROSS TERMINAL
6
OF LOW VOLTAGE STRIP & BROWN WIRE
TO PRIMARY CONTROL PLUG (JP1−1)?
NO
REPAIR WIRING CONNECTION
BETWEEN LIMIT & PRIMARY
CONTROL PLUG
(BROWN WIRE).
REPAIR WIRING CONNECTION BETWEEN PRIMARY
CONTROL & R SIDE OF TRANSFORMER.
YES
YES
CHECK FOR HEAT DEMAND AT UNIT. IS 24VAC
PRESENT ACROSS TERMINALS C & W ON
LOW VOLTAGE STRIP?
YES
SEE GAS CHECKS ON
NEXT PAGE.
YES
C
YES
7
IS 24VAC PRESENT ACROSS
TERMINAL C OF LOW VOLTAGE
STRIP & BLUE WIRE TO PRIMARY
CONTROL PLUG (JP1−4)?
NO
YES
REPLACE
PRIMARY
CONTROL.
YES