AC Tripping Breaker

A failed run capacitor causes the compressor or fan motor to draw excessive startup current. The breaker sees an overload condition and trips for protection. Often happens at startup, not during normal operation.

Trips immediately or within 30 seconds of starting. Hum from outdoor unit. Test capacitor with multimeter — more than 6% below labeled MFD = failed.

Compressor motor windings have shorted to the metal housing. Massive current flow trips the breaker instantly. This is mechanical failure — the compressor is finished.

Breaker trips IMMEDIATELY at startup, every time. May smell burning electronics. Megger test (insulation resistance) confirms — but typically diagnosed by an HVAC tech.

Breakers degrade over time, especially after multiple trip events. A weak breaker trips below its rated amperage. Common in 20+ year-old electrical panels.

Compare AC's amp draw (clamp meter, professional measurement) to breaker rating. If AC pulls within rating but breaker still trips, the breaker is the problem.

Heavily fouled outdoor coils cause high head pressure, increasing compressor amp draw. Eventually amperage exceeds breaker rating, especially in hot weather. System may run fine in cool weather, trip in summer.

Trips only when outdoor temp is high (95°F+). Visual inspection of outdoor unit shows debris-clogged fins.

Loose connection at the breaker, disconnect box, or outdoor unit creates arcing and intermittent shorts. Can also be rodent damage to wiring inside the disconnect or whip.

Random trips not tied to startup or runtime. Smell of ozone or burning near electrical connections. Visible damage to wiring insulation.

Contactor with welded contacts keeps the compressor energized continuously. Without proper cycling, the compressor overheats and the breaker eventually trips on thermal overload.

AC runs when thermostat is set to OFF (only disconnect stops it). Visible burn marks on contactor.