Lennox G21Q Series Installation Instructions Manual page 21

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
REPLACE
TRANSFORMER.
NO
DETERMINE CAUSE OF OPEN LIMIT
AND/OR REPLACE IF DEFECTIVE.
G21 TROUBLESHOOTING FLOW CHART
(continued from flow chart on previous page)
NOTE—Numbered steps refer to illustrations on next to last page.
UNIT WILL NOT RUN
ELECTRICAL
IS THERMOSTAT PROPERLY SET?
CHECKS
NO
CHECK FOR 120VAC POWER TO UNIT & ADEQUATE GROUNDING.
(GROUNDING REQUIRED FOR PROPER OPERATION OF IGNITION SYSTEM.)
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.
NO
FUSE.
REPLACE SWITCH.
SYSTEM MAY BE LOCKED OUT. TURN THERMOSTAT HEATING DEMAND
OFF AND ON AGAIN. NOTE—CONTINUE THROUGH TROUBLESHOOTING
FLOW CHART TO LOCATE REASON FOR LOCKOUT.
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
INTERNAL AND EXTERNAL TO UNIT. REPAIR
ANY LOOSE OR DAMAGED CONNECTIONS.
TURN ON POWER. SET THERMOSTAT FOR HEAT DEMAND.
IS 24VAC PRESENT ACROSS TERMINAL C
6
OF LOW VOLTAGE STRIP & BROWN WIRE
NO
REPAIR WIRING CONNECTION
BETWEEN LIMIT & PRIMARY
CONTROL PLUG
(BROWN WIRE).
REPAIR WIRING CONNECTION BETWEEN PRIMARY
CONTROL &
3DJH 
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
CHECK ALL WIRING CONNECTION
TO PRIMARY CONTROL PLUG (JP1--1)?
YES
7
IS 24VAC PRESENT ACROSS
TERMINAL C OF LOW VOLTAGE
STRIP & BLUE WIRE TO PRIMARY
CONTROL PLUG (JP1--4)?
NO
SIDE OF TRANSFORMER.
R
YES
YES
REPLACE
PRIMARY
CONTROL.