HVACopediaGoodman · Furnace troubleshooting
Reversed line polarity
What is going on
A polarity error means hot and neutral are swapped at the furnace, or the ground isn't good. The board checks it before it'll run, so it stays locked out until it's right. You see it a lot on new installs or after someone changed a plug-in or a receptacle.
Likely causes
- 115 V AC polarity reversed
- Poor unit ground
- Wiring mistake at the disconnect or junction box
Check in this order
- Turn power off before service.
- Review the wiring diagram and correct the polarity.
- Verify the ground and correct if needed.
- Check the wiring at the disconnect and junction box and fix anything that's swapped.
- Restore power and confirm the error clears on the next call for heat.
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)
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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.