HVACopediaCarrier · Furnace
21.1 24 VAC on gas valve when it should be off
What the control is telling you
The control detects 24 VAC at the gas valve circuit when no gas valve output should be present.
Applies to: Carrier 59SC6A
Likely causes
- Gas valve relay on control stuck or failed
- Miswired or shorted gas valve circuit
Test and repair steps
- Warning: Shut off gas to the furnace immediately if burners stay lit with no call for heat.
- Remove the thermostat call and measure voltage at the gas valve terminals.
- Inspect gas valve wiring for shorts or miswiring.
- If 24 VAC remains on the valve with no call and wiring is correct, replace the furnace control.
- Program any new control with the Model Program Number on the rating plate (app via NFC or correct super plug).
Settings for these units
Filter sizes by casing width and filter cabinet · 59SC6A
| Location | Size | Side return filter | Bottom return filter | Type |
|---|---|---|---|---|
| Furnace casing | 14-3/16 in. wide | 16 x 25 x 3/4 in. | 14 x 25 x 3/4 in. | Washable |
| Furnace casing | 17-1/2 in. wide | (1) 16 x 25 x 3/4 in. | (1) 16 x 25 x 3/4 in. | Washable |
| Furnace casing | 21 in. wide | (1) 16 x 25 x 3/4 in. | (1) 20 x 25 x 3/4 in. | Washable |
| Furnace casing | 24-1/2 in. wide | (1) 16 x 25 x 3/4 in. | (1) 24 x 25 x 3/4 in. | Washable |
| Filter cabinet | 16 in. high | (1) 16 x 25 x 3/4 in. or (1) 16 x 25 x 4-5/16 in. | - | Washable or media |
| Filter cabinet | 20 in. high | (1) 20 x 25 x 3/4 in. or (1) 20 x 25 x 4-5/16 in. | - | Washable or media |
| Filter cabinet | 24 in. high | (1) 24 x 25 x 3/4 in. or (1) 24 x 25 x 4-5/16 in. | - | Washable or media |
Side-return filters can differ in size - measure the existing filter.
Every return-air inlet needs a filter.
Minimum clearances to combustibles · 59SC6A
| Position | Minimum clearance |
|---|---|
| Rear | 0 |
| Front (combustion air openings in furnace and in structure) | 1 in. (25 mm) |
| Required for service | 24 in. (610 mm) (see note) |
| All sides of supply plenum | 1 in. (25 mm) (see note) |
| Sides | 0 |
| Vent | 0 |
| Top of furnace | 1 in. (25 mm) |
Service and supply-plenum values are marked 'consult local building codes'.
Keep 1 in. (25 mm) from combustibles to supply ductwork for 36 in. (914 mm) horizontally from the furnace.
Models that show this code
11 models in 59SC6A
Other codes on the same units
- 13.1 Limit lockout - main limit open over 3 minutes
- 14.1 Ignition lockout after 4 tries
- 14.2 Lockout - flame lost 3 times after 70 s of heating
- 14.3 Lockout - 7 flame-loss events in one heat call
- 22.1 False flame
- 23.1 Main pressure switch stuck closed
- 23.2 Secondary pressure switch stuck closed
- 24.1 Fuse fault (24 V)
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Source: Carrier 59SC6A Installation, Start-up, Operating and Service Instructions, Fig. 60 Service Label Information, p.54. Summarized in our own words; check the original manual for your model.
Homeowner looking at this code? See what it means for you and when to call a technician.
For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.