Lennox G21Q Series Installation Instructions Manual page 23

G21 TROUBLESHOOTING FLOW CHART — UNIT WILL NOT RUN
CHECK VOLTAGE AT TERMINAL AND
CHECKING THERMOSTAT DEMAND
THERMOSTAT
WIRING
24VAC
WITH DEMAND?
R
2
CHECKING VOLTAGE AT GAS VALVE
GAS VALVE
CHECKING FOR OPEN SWITCH
DIFFERENTIAL
PRESSURE SWITCH
R x 1
READ 0 PHMS
FOR CONTINUITY
4
CHECKING FOR OPEN SWITCH
IN LIMIT CONTROL
PRIMARY
LIMIT CONTROL
BROWN
LIMIT
TRACE LIMIT WIRE TO
WIRES
CONTROL BOX. WIRE NUT
CONNECTION FOR METER
LEAD TEST POINT.
LOW VOLTAGE TERMINAL
STRIP WITH FUSE
LOCATED ON CONTROL BOX 24VAC
POWER?
FUSE
W Y G C
24VAC DURING
IGNITION TRIALS?
3
FLUE
INTAKE
AIR INTAKE CHAMBER
FLUE
AIR
INTAKE
AIR INTAKE CHAMBER
5
R x 1
READ 0 OHMS
FOR CONTINUITY
CHECKING VOLTAGE AT PRIMARY CONTROL
PRIMARY CONTROL
WIRING HARNESS PLUG (JP1)
!
WIRING
$
HARNESS
1
LOW VOLTAGE TERMINAL
STRIP WITH FUSE
LOCATED ON CONTROL BOX
THERMOSTAT
WIRING
CHECKING VOLTAGE AT PURGE BLOWER
9
120VAC?
RED*
AIR
!
WIRING $
HARNESS
IT IS NORMAL FOR THE ELECTRODE TO
PROTRUDE AT AN UNUSUAL ANGLE
SPARK PLUG GAP
0.115” + 0.000”
10
NOTE- - CARBON RESISTOR TYPE PLUGS
3DJH 
# "
24VAC?
7
R W
WHITE (NEUTRAL)
PURGE BLOWER
PRIMARY CONTROL
WIRING HARNESS PLUG (JP1)
# "
*NOTE--RED WIRE GOES TO PRIMARY
CONTROL HARNESS JP1--5.
SPARK PLUG
— 0.010”
APPROX. 45
CERAMIC
RESISTOR
TYPE
CHAMPION FI- -21500
SHOULD NOT BE USED.
24VAC?
6
Y G C
120VAC?
8
-