Fault 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 access panel. — — 2
2. Is secondary voltage fuse blown? Check continuity to make sure. 5 3 —
3. Replace furnace control board. —— 4
4. Go to page number indicated in Index for CLEANUP AND START-UP INSTRUCTIONS. — — INDEX
5.
Disconnect all thermostat leads from furnace control board (including HUM terminal) and replace
secondary voltage fuse.
—— 6
6. Depress door switch. Use a piece of tape to hold switch closed. — — 7
7. Does Fault Code 24 flash? 810 —
8.
You have a short circuit in limit switch circuit. This includes limit switch, flame rollout switch, and
auxiliary limit switch.
—— 9
9. Fix problem and replace secondary voltage fuse if necessary. — — 4
10. Jumper R and W/W1 thermostat terminals on furnace control board. — — 11
11. Does Fault Code 24 occur when W/W1 is energized? 12 16 —
12.
Disconnect jumper wire across R and W/W1 thermostat terminals and replace secondary voltage
fuse.
—— 13
13.
Disconnect PL2 from furnace control board and jumper R and W/W1 thermostat terminals on fur-
nace control board.
—— 14
14. Does Fault Code 24 occur when W/W1 is energized? 3 15 —
15. You have a short circuit in pressure switch circuit. — — 9
16. Does Fault Code 24 occur when low-pressure switch is energized? 17 20 —
17. Disconnect PL2 from furnace control board. — — 18
Table 2—Air Conditioning (A/C) Airflow Setup Switch Position
AIR CONDITIONER
(TONS)
AIRFLOW
(CFM)
A/C SWITCH POSITION ALLOWABLE FURNACE MODEL SETUP
A/C-1 A/C-2 A/C-3 040 060 080 080 100 120
Default
1200 or
2000
OFF OFF OFF
3 Tons
1200 CFM
3 Tons
1200 CFM
3 Tons
1200 CFM
5 Tons
2000 CFM
5 Tons
2000 CFM
5 Tons
2000 CFM
1-1/2 600 ON OFF OFF X X X — — —
2 800OFFONOFFXXXXXX
2-1/2 1000 ON ON OFF XXXXXX
3 1200 OFF OFF ON XXXXXX
3-1/2 1400 ON OFF ON XXXXXX
4 1600 OFF ON ON — — — X X X
5 2000 ON ON ON — — — X X X
X—Indicates allowable selection.
Table 3—Continuous Fan (CF) Airflow Setup Switch Position
CONTINUOUS FAN
(CFM)
CF SWITCH POSITION ALLOWABLE FURNACE MODEL SETUP
CF-1 CF-2 CF-3 040 060 080
080
(5 Ton)
100 120
Default OFF OFF OFF 565* 515* 690* 690* 860* 1035*
600 ON OFF OFF X X X — — —
800 OFF ON OFF X X X X X X
1000 ON ON OFF X X X X X X
1200 OFF OFF ON X X X X X X
1400 ON OFF ON X X X X X X
1600 OFF ON ON — — — X X X
2000 ON ON ON — — — X X X
* Add 15% additional CFM when Bypass Humidifier switch SW-3 on control board is used.
X—Indicates allowable selection.
Table 4—Two-Speed AC/HP Airflow Requirements (CFM)
OUTDOOR UNIT CAPACITY 036 048 060
A/C Setting 3 Tons—1200 4 Tons—1600 5 Tons—2000
CF Setting 800 1000 1000
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