17
STEP
ACTION
YES
NO
GO TO
27.
Disconnect jumper wire across R and W/W1 thermostat terminals and replace secondary
voltage fuse.
28
28.
Disconnect BLUE wire to gas valve GV and jumper R and W/W1 thermostat terminals.
29
29.
Does status code 34 flash? If not, status code 24 should occur when BLUE wire is ener-
gized.
33
30
30.
Turn power off and disconnect PL1 from variable speed furnace control.
31
31.
Do you have continuity between the BLUE wire and chassis ground?
32
3
32.
The BLUE wire to gas valve GV is shorting to ground. Replace or repair it.
11
33.
Replace gas valve GV.
4
34.
Turn power off and disconnect PL1 from variable speed furnace control.
35
35.
Do you have continuity between the GRAY wire connected to the high heat pressure
switch HPS and chassis ground?
36
3
36.
You have a short circuit in the high heat pressure switch circuit.
11
37.
Reconnect the pressure tube from the pressure switch assembly back to the collector box.
38
38.
Does status code 24 begin flashing when the high heat pressure switch HPS is energized?
39
56
39.
Disconnect jumper wire across R, W/W1, and W2 thermostat terminals and replace second-
ary voltage fuse.
40
40.
Disconnect BROWN wire to gas valve GV and jumper R, W/W1, and W2 thermostat ter-
minals.
41
41.
Does status code 24 begin flashing when the high heat pressure switch HPS is energized?
42
33
42.
Turn power off and disconnect PL1 from variable speed furnace control.
43
43.
Do you have continuity between the BROWN wire and chassis ground?
44
3
44.
The BROWN wire to high heat pressure switch HPS and gas valve GV is shorting to
ground. Replace or repair it.
11
45.
Disconnect jumper wire across R, W/W1, and W2 thermostat terminals and wait until
blower stops.
46
46.
Jumper R, G, and Y/Y2 thermostat terminals.
47
47.
Does status code 24 begin flashing when G and Y/Y2 are energized?
3
48
48.
Reconnect User Interface ABCD connector (if used) or all thermostat leads (if used) to the
variable speed furnace control. Do not reconnect the humidifier lead to HUM terminal.
Operate the furnace in heating and cooling mode from thermostat.
49
49.
Does status code 24 occur during heating cycle?
50
51
50.
You have a defective thermostat or a short circuit in the wiring between thermostat and
furnace. If the furnace is twinned, also check the twinning kit relay TKR.
11
51.
Does status code 24 occur during cooling cycle?
52
53
52.
You have a defective thermostat or a short circuit in the wiring between thermostat and
outdoor unit, or a short circuit in the outdoor unit contactor or reversing valve(heat pump
only).
11
53.
Does problem usually occur in cooling mode?
54
55
54.
Check outdoor unit contactor. Failure to pull in can cause excessive current draw on low--
voltage circuit. This can be an intermittent problem.
11
55.
Reconnect humidifier and check for excessive current draw when the blower turns ON. If
current draw is excessive check wiring to humidifier solenoid, diode bridge(if used), and
humidifier solenoid.
11
56.
Continue to observe the furnace operation for 10 minutes.
57
57.
Does status code 24 flash after the blower comes on?
58
59
58.
The insulation is loose and has shorted against the limit switch(es).
11
59.
Check for loose or torn insulation because it can cause intermittent occurrences of status
code 24.
45
