HVACopedia

All brands · Electrical troubleshooting

Any circuit fault — classify the problem

What is going on

Load dead, breaker trips, fuse blows, shocks, low voltage at load.

Likely causes

  • Short circuit
  • Ground fault
  • Overload
  • Unintentional voltage drop
  • Open circuit

Check in this order

  1. Short = instant trip, near-zero resistance around the load
  2. Ground fault = energized metal, GFCI trips, ohms from hot to ground
  3. Overload = current above rating following the normal path, breaker trips slowly or not at all (too many parallel loads, wrong supply, strained equipment, failing component)
  4. Voltage drop = voltage at panel vs at unit differ by more than ±10% (long/undersized wire, poor connections, bad contacts)
  5. Open = full applied voltage across the component, zero amps (broken wire, blown fuse/breaker, burnt component, bad connection)

More electrical guides

Related

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: General HVAC service practice — verify per model. 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.