Status Code 24
SECONDARY VOLTAGE FUSE IS OPEN—INDICATES FUSE IS OPEN, AND THERE IS A SHORT IN LOW-VOLTAGE WIRING.
STEP
ACTION
YES
NO
GO TO
1.
Turn power off and remove blower door.
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2
2.
Is secondary voltage fuse blown? Check continuity to make sure.
5
3
—
3.
Replace 2-stage furnace control.
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4
4.
Replace secondary voltage fuse if necessary, then go to page number indicated
in Index for CLEANUP AND START-UP INSTRUCTIONS.
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INDEX
5.
Disconnect all thermostat leads from 2-stage furnace control (including all wires
connected to HUM terminal) and replace secondary voltage fuse. On variable-
speed units, disconnect WHITE wires from HUM terminal on 2-stage furnace
control, and disconnect Y1 and O thermostat leads in blower compartment (if
used).
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6
6.
Replace fuse. Turn power on and depress door switch. Use a piece of tape to
hold switch closed.
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7
7.
Does status code 24 flash?
8
12
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8.
Turn power off and disconnect PL1 from 2-stage furnace control.
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9
9.
Do you have continuity between either RED wire connected to limit switch LS
and chassis ground?
10
76
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10.
You have a short circuit in limit switch circuit. This includes limit switch and
flame rollout switch.
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—
11
11.
Fix problem.
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4
12.
Disconnect pressure tube from collector box. Jumper R and W/W1 thermostat
terminals.
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13
13.
Does status code 24 begin flashing when W/W1 is energized?
14
21
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14.
Turn power off and disconnect PL1 from 2-stage furnace control.
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15
15.
Do you have continuity between ORANGE wire connected to low-heat pressure
switch LPS and chassis ground?
16
17
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16.
You have a short circuit in low-heat pressure switch circuit. This includes draft
safeguard switch DSS and auxiliary limit switches ALS1, 2 (if used).
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11
17.
Do you have continuity between GRAY wire connected to high-heat pressure
switch HPS and chassis ground?
18
3
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18.
Disconnect PL2 from 2-stage furnace control.
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19
19.
Do you have continuity between PL2-2 and PL1-10 on 2-stage furnace control.
3
20
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20.
You have a short circuit in either GRAY wire connected to high-heat pressure
switch HPS or GRAY wire connected between PL1-9 and PL2-2
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—
11
21.
Reconnect pressure tube from pressure switch assembly back to collector box.
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22
22.
Does status code 24 begin flashing when low-heat pressure switch LPS is ener-
gized?
23
26
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23.
Turn power off and disconnect PL1 from 2-stage furnace control.
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24
24.
Do you have continuity between YELLOW wire connected to low-heat pressure
switch LPS and chassis ground?
25
3
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25.
The YELLOW wire from low-heat pressure switch LPS is shorting to ground.
Replace or repair it.
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—
11
26.
Does status code 24 begin flashing when gas valve GV is energized?
27
34
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27.
Disconnect jumper wire across R and W/W1 thermostat terminals and replace
secondary voltage fuse.
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28
28.
Disconnect BLUE wire to gas valve GV. Jumper R and W/W1 thermostat termi-
nals.
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29
29.
Does status code 34 flash? If not, status code 24 should occur when BLUE wire
is energized.
33
30
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30.
Turn power off and disconnect PL1 from 2-stage furnace control.
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31
31.
Do you have continuity between BLUE wire and chassis ground?
32
3
—
32.
The BLUE wire to gas valve GV is shorting to ground. Replace or repair it.
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11
33.
Replace gas valve GV.
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4
34.
Disconnect jumper wire across R and W/W1 thermostat terminals and wait until
inducer stops.
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35
35.
Jumper R, W/W1, and W2 thermostat terminals.
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36
36.
Does status code 24 begin flashing when high-heat pressure switch HPS is en-
ergized?
37
79
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37.
Disconnect jumper wire across R, W/W1, and W2 thermostat terminals and re-
place secondary voltage fuse.
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38
38.
Disconnect BROWN wire to gas valve GV. Jumper R, W/W1, and W2 thermo-
stat terminals.
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39
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