Ignition Control Checkout Gc3; Is Green Diagnostic Led Lit? - Lennox G21Q3-40 Unit Information

LIT
Control should operate properly. Pro
ceed to UNIT WILL NOT RUN"−GAS
CHECKS AND SPARK CHECKS to
rule out other possibilities.
If 24 VAC is present between JP72−4 and Common and
LED is not lit, reset power to control. If control still
does not operate, replace control.
LIT
Control should operate properly. Pro
ceed to UNIT WILL NOT RUN"−GAS
CHECKS AND SPARK CHECKS to
rule out other possibilities.
YES
If 24 VAC is present between JP72−4
and Common and LED is not lit, re
set power to control. If control still
does not operate, replace control.

IGNITION CONTROL CHECKOUT GC3

START HERE

IS GREEN DIAGNOSTIC LED LIT?

Does control A3 have 24VAC
supplied between pins JP72−4
and Common?
YES
IGNITION CONTROL CHECKOUT G891
START HERE
IS GREEN DIAGNOSTIC LED LIT?
Does control A3 have 24VAC
supplied between pins JP72−4
and Common?
ELECTRICAL CHECKOUT.
NOT LIT
Turn off unit power at disconnect for at least 3
seconds. Then turn power back on. Allow 3 sec
onds for control to power−up. Control should op
erate properly, proceed to UNIT WILL NOT
RUN"−GAS CHECKS AND SPARK CHECKS to
Proceed to
ELECTRICAL CHECKOUT.
NOT LIT
(0.5 Seconds on, 2.5 seconds off
Turn off unit power at disconnect for at least 3
seconds. Then turn power back on. Allow 3 sec
onds for control to power−up. Control should
operate properly, proceed to UNIT WILL NOT
RUN"−GAS CHECKS AND SPARK CHECKS to
(0.1 seconds on, 0.1 seconds off)
NO
Check sensor wire for breaks or shorts to
ground and for loose connections to con
trol and/or sensor Check flame signal.
Proceed to
1. Was sensor tight when removed?
2. Are cracks present in porcelain?
3. Make ohmmeter check between sensor
termination and center rod. Replace if open.
4. Does the center rod have a coating?
Clean or replace sensor if resistance is above 35 ohms.
Install sensor back in unit. Turn on power. Restart unit.
Page 58
FLASHING
rule out other possibilities.
NO
FLASHING
rule out other possibilities.
Turn off power
Remove and check sensor
(use 11/16" sensor socket)