AC Breaker Keeps Tripping: How to Find Out Why

By HVAC Cheat Sheet Team · 3 min read

A tripping breaker is the system telling you something is drawing too much current. Resetting it over and over can turn a fixable problem into a burned-up compressor or melted wiring.

Safety: Treat everything as live until you've locked out the breaker and verified zero volts. A grounded compressor can energize the cabinet. Don't keep resetting the breaker to "see if it holds."

When does it trip?

When it trips Points to
Instantly on reset, with the thermostat off Short in the wiring, disconnect or contactor line side
Instantly when the contactor pulls in Grounded or shorted compressor or fan motor
A few seconds into a start attempt Locked rotor, failed capacitor, low voltage, unequal pressures
After running a while High amps: dirty condenser, failed fan, overcharge, high voltage drop, or a weak breaker
Randomly, on hot days High head pressure, weak breaker, loose connections heating up

Step by step

  1. Lock out the breaker and verify zero volts at the disconnect.
  2. Look for damage: burned wires, melted insulation, chewed wires, a burned contactor.
  3. Test the compressor windings to ground with a megohmmeter (or at least an ohmmeter) from each terminal (C, S, R) to a clean copper line or ground. Any low reading means a grounded compressor. See AC compressor not starting.
  4. Test the fan motor leads to ground the same way.
  5. Check the windings of the compressor (C–S + C–R ≈ S–R) and the fan motor.
  6. Test the run capacitor. See how to test a run capacitor.
  7. Check the wiring from the panel to the disconnect to the unit for damage and loose lugs.
  8. If everything tests clean, reset the breaker and measure:
    • Voltage at the unit, including during the compressor start
    • Starting current and running amps against the nameplate (RLA, LRA, FLA)
    • Head pressure, to catch a dirty condenser or failed fan. See how to clean a condenser coil.
  9. Check the breaker itself: is it sized per the nameplate MOP (maximum overcurrent protection)? Is it hot or loose in the panel? Breakers do wear out, but rule out the unit first.

Common causes

  • Grounded compressor: an internal short to the shell. The compressor needs replacing; check for acid after a burnout.
  • Locked rotor: the compressor draws locked-rotor amps and trips the breaker or its overload. Check the capacitor and voltage first.
  • Shorted condenser fan motor.
  • Failed run capacitor: the compressor struggles to start and draws high current.
  • High head pressure: a dirty condenser, a failed fan motor, overcharge or non-condensables raise amps until the breaker trips.
  • Wiring problems: loose lugs, damaged conductors, or a wire rubbing through on the cabinet.
  • Undersized or worn breaker: compare with the nameplate MOP and MCA.

Common mistakes

  • Resetting the breaker repeatedly. Every reset on a grounded compressor does more damage.
  • Replacing the breaker first. It's usually the load.
  • Skipping the insulation-to-ground test because the windings read OK between terminals.
  • Not finding the cause of a compressor failure before replacing it.

FAQ

Is it dangerous if my AC keeps tripping the breaker?

It can be. A grounded compressor or damaged wiring can be a shock or fire hazard. Turn the system off and have it checked.

Can a bad capacitor trip a breaker?

Yes. Without a working capacitor, the compressor or fan motor may not start and draws high current until the breaker or overload trips.

Can a dirty outdoor unit trip the breaker?

Yes. A dirty condenser raises head pressure and compressor amps, especially on hot days.

Sources

Parts:CompressorCondenser Fan MotorRun CapacitorContactor
Symptoms:Blown Fuse or Tripping BreakerOutdoor Unit Won't StartAC Not Cooling

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Field reference for trained technicians. Always follow the equipment manufacturer's instructions, local code and safe work practices. See our editorial standards, or report a correction.