Electrical Testing; Check Voltage At Terminal And Checking Thermostat Demand; Checking Voltage At Gas Valve; Checking Voltage At Primary Control - Lennox G21Q3-40 Unit Information

CHECK VOLTAGE AT TERMINAL AND
CHECKING THERMOSTAT DEMAND
LOW VOLTAGE TERMINAL STRIP WITH 3 AMP FUSE
LOCATED ON CONTROL BOX
24VAC
WITH DEMAND?
NM
W1
W2
2

CHECKING VOLTAGE AT GAS VALVE

GAS VALVE
CHECKING FOR OPEN SWITCH
DIFFERENTIAL
PRESSURE SWITCH
R x 1
READ 0 OHMS
FOR CONTINUITY
4
CHECKING FOR OPEN SWITCH
IN LIMIT CONTROL
PRIMARY
LIMIT CONTROL
ORANGE
LIMIT
TRACE
WIRES
CONTROL BOX. WIRE NUT
CONNECTION FOR METER
LEAD TEST POINT.
MANUAL−RESET
SECONDARY LIMIT*
REVERSE FLOW
APPLICATION ONLY
*Secondary limit on CGA
units may be
manual−reset or
auto−reset.

ELECTRICAL TESTING

24VAC
POWER?
G R C
DS
Y1
Y2
24VAC DURING
IGNITION TRIALS?
3
TO FLUE
AIR
INTAKE
AIR INTAKE CHAMBER
TO FLUE
AIR
INTAKE
AIR INTAKE CHAMBER
LIMIT WIRE TO
5
R x 1
READ 0 OHMS
FOR
CONTINUITY

CHECKING VOLTAGE AT PRIMARY CONTROL

PRIMARY CONTROL
WIRING HARNESS PLUG (JP1)
3 2
6 5
1
LOW VOLTAGE TERMINAL
STRIP WITH 3 AMP FUSE
LOCATED ON CONTROL BOX
CHECKING VOLTAGE AT PURGE BLOWER
9
120VAC?
RED*
3
6
WIRING
HARNESS
10
It is normal for the
electrode to protrude
at an unusual angle
NOTE− CARBON RESISTOR TYPE
Page 61
24VAC?
1
4
24VAC?
7
G R
NM
W1
W2
WHITE (NEUTRAL)
PURGE BLOWER
PRIMARY CONTROL
2
1
WIRING HARNESS PLUG
(JP72)
5 4
*NOTE−RED WIRE GOES
TO PRIMARY CONTROL
HARNESS JP72−5.
SPARK PLUG
GAP
0.115" +0.000"
−0.010"
CHAMPION FI 21500
or equivalent only
PLUGS
SHOULD NOT BE USED.
6
C
DS
Y1
Y2
120VAC?
8
APPROX. 45°
CERAMIC
RESISTOR
TYPE