HVACopedia

Carrier · Furnace troubleshooting

Furnace not responding to thermostat - Carrier 58SB0A/58SB1A

What is going on

No heat or cool response although the control has power. Flowchart-based checks for the single-stage 58SB control.

Likely causes

  • Thermostat or thermostat cable fault
  • No 24 V reaching W, Y or G
  • Thermostat not compatible with the control input
  • Failed furnace control

Check in this order

  1. Confirm the amber LED is on steady; if dark, check breaker, door switch, 115 V at L1/L2 and 24 V at SEC-1/SEC-2.
  2. Rapid flashing with no pause means reversed 115 V polarity or, on twinned units, transformer phasing.
  3. Read the stored code briefly pull a draft safeguard switch wire until the LED goes out (under 4 s), then count the code flashed 4 times.
  4. Measure 24 V at W, Y and G with a call; none means the thermostat or cable is at fault.
  5. If 24 V is there but the control ignores it, replace the control.
  6. If the problem goes away with a jumper in place of the thermostat, the thermostat is incompatible: fit a ballast resistor or connect the thermostat C wire to COM-24V.

Applies to: Carrier 58SB0A, 58SB1A

More furnace guides

Related

Carrier error codes · Carrier tips · Calculators and reference tables

Take it to the job

All guides, error codes and tips work offline in the HVACopedia app.

Open the app

Source: Carrier 58SB0A-05SI installation manual (text export), Fig. 51 Troubleshooting Guide. Written in our own words; check the manual for your exact model.

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.