HVACopediaGoodman · Furnace troubleshooting
Open fuse, no furnace operation
What is going on
The furnace is dead or won't run, and the 3-amp control fuse on the board has blown. That fuse protects the 24 V side, so a blown one almost always means something is shorting in the low voltage wiring. Just swapping the fuse usually gets you another blown fuse a minute later.
Likely causes
- Open fuse
- Short in low voltage wiring, such as a pinched or chafed thermostat wire, a staple through the cable, or a bad accessory like a humidifier or relay
Check in this order
- Turn power off before repair.
- Locate and correct the short in the low voltage wiring.
- Look along the thermostat wire runs and at the cabinet edges where the wire passes through. Disconnect any add-ons one at a time to see if one is the cause.
- Replace the fuse with a 3-amp automotive type fuse.
- Restore power and watch the furnace through a full cycle.
Applies to: 34.5 in chassis gas furnaces
More furnace guides
- Airflow lower than demanded, furnace runs on low stage when high stage is expected
- Alternate combustion air opening (upflow or horizontal)
- Alternate vent/flue location (upflow or horizontal left)
- Annual inspection checklist
- Auxiliary limit control (location and purpose)
- Auxiliary limit switch open (blower compartment)
Take it to the job
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Source: Goodman GMVC96 Service and Troubleshooting, p. 61. 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.