Why does my AC trip the breaker?

An AC breaker trips when the compressor load is more than the circuit can safely carry

An air conditioner is a motor load, and motor loads behave differently from lights or receptacles. The outdoor condenser may run at a reasonable current once it is up to speed, but the compressor can pull a much higher inrush current for a split second when it starts. That starting surge is why a breaker may trip exactly when the thermostat calls for cooling, even though the AC ran fine earlier in the season.

The first thing to note is the timing:

• Trips instantly when cooling starts: possible compressor short, locked rotor, shorted wire, failed contactor, or wrong breaker size.
• Trips after a few seconds: compressor may be struggling to start, capacitor may be weak, or voltage may be dropping under load.
• Trips after 10–30 minutes: overheating equipment, loose termination, weak breaker, dirty condenser coil, or overloaded circuit.
• Trips only on very hot days: the AC is working at its hardest, and a marginal circuit or compressor fault shows up.
• Trips when other loads run too: the panel or service may need a load calculation, especially with an EV charger, range, dryer, hot tub, or heat pump in the home.

For central AC, the outdoor unit nameplate matters. It usually lists electrical values such as minimum circuit ampacity and maximum overcurrent protection. The breaker and wire must match the equipment listing and the Ontario Electrical Safety Code, not just whatever breaker happens to be available in the panel.

If the breaker trips once during a storm or after a utility blink, reset it one time. If it trips again, stop. Repeated resets can turn a correct safety trip into overheated wiring or damaged equipment. If the breaker will not stay on at all, see why a breaker will not reset and leave it off until it is checked.

The electrical causes are usually the circuit, breaker, panel connection, or load calculation

The electrical side of an AC trip is about whether the wiring system can safely supply the load the air conditioner is asking for. We separate that from an HVAC fault before replacing parts.

Common electrical causes include:

A central air conditioner should not be sharing a general-purpose receptacle circuit. It normally needs its own properly sized branch circuit from the panel to an outdoor disconnect near the condenser. If your AC was added after the house was built, the original panel may not have been planned for today’s load: AC, induction cooking, EV charging, basement suite equipment, hot tub, and electric dryer all competing for capacity.

A load calculation is especially important when the breaker trips only during combined use. For example, the AC may run until the dryer, oven, and EV charger are all active. That does not automatically mean the AC is defective. It may mean the service has no realistic headroom, or the panel has been filled in a way that needs correction.

If the fix is a new circuit, a straightforward 20A dedicated run in the GTA often falls around $250–$500, depending on distance and access. Larger 30A–50A runs are commonly in the $400–$900 range. For an air conditioner, the final breaker and wire size must come from the equipment nameplate and site conditions, so City Power quotes it in writing after a site visit. City Power Electrical Services is a Licensed Electrical Contractor, ECRA/ESA #7015314, and files ESA notifications where required.

For circuit work, see dedicated circuit installation.

HVAC equipment faults can trip a good breaker, so the AC unit itself must be ruled out

A tripping breaker does not automatically mean the panel is bad. The breaker may be doing exactly what it is designed to do: opening the circuit because the AC equipment has a fault.

HVAC-side causes include a failing compressor, seized fan motor, shorted contactor, weak capacitor, dirty condenser coil, refrigerant-related operating problems, or internal wiring damage inside the outdoor unit. A weak capacitor is a common starting problem: the compressor struggles to get moving, current rises, and the breaker trips. A dirty outdoor coil can also make the unit run hotter and draw more current than normal during a heat wave.

Here is the practical split:

• Call an electrician first if the breaker is hot, loose, wrong for the panel, recently changed, tripping with other loads, or connected to old/damaged wiring.
• Call HVAC first if the outdoor fan does not spin, the compressor hums and stops, the condenser is iced or extremely dirty, or the AC trips only when the compressor engages.
• Call both trades if needed when the electrical supply tests correctly but the HVAC contractor finds a compressor or motor fault that needs verified power and disconnect work.

The outdoor disconnect is part of the electrical path and should be checked. So should the flexible whip from the disconnect to the condenser. We often see cracked outdoor fittings, moisture entry, UV-damaged conductors, missing bushings, or a loose ground in older installations. Those are not thermostat problems; they are electrical defects that can make a breaker trip or create shock risk around the condenser.

Do not upsize the breaker to “get through the summer.” If a 20A breaker trips, replacing it with a 30A breaker without confirming the conductor size and equipment rating can overheat the wiring. The breaker protects the wire, and the AC nameplate limits the maximum overcurrent device. Bigger is not safer.

If your breaker is making noise or vibrating while the AC is trying to start, treat that as a separate warning sign and read why a breaker is buzzing.

The safe troubleshooting order is reset once, reduce load, then test before replacing parts

You can do a few safe checks before booking service, but do not open the panel or condenser unless you are qualified. The goal is to collect useful information without defeating the breaker’s protection.

Start here:

• Turn the thermostat to off.
• Check whether the breaker handle is fully tripped or sitting in the middle.
• Reset the breaker once by moving it fully off, then back on.
• Turn the AC back on and note exactly when it trips.
• Make sure the outdoor condenser is clear of leaves, cottonwood fluff, storage bins, or shrubs.
• Turn off avoidable large loads for the test, such as the dryer or EV charger.
• Write down whether the indoor blower keeps running after the outdoor unit trips.

If the breaker trips immediately again, leave it off. If it runs only with other appliances off, that points toward capacity or voltage drop, not necessarily a bad compressor. If it runs for a while and then trips, heat is a clue: loose terminations, a weak breaker, a labouring compressor, or poor condenser cooling all become more obvious after warm-up.

An electrician’s diagnosis usually includes checking the AC nameplate, breaker rating, conductor size, disconnect, voltage under load, visible heat damage, torque/termination condition where accessible, grounding and bonding, and whether the circuit was altered without an ESA notification. On older panels, the breaker must also be the correct listed type for that panel. A breaker that physically fits is not automatically approved for that equipment.

For a new AC circuit, panel correction, or breaker replacement, ESA inspection may be required. The inspector is not tuning the AC; they are checking that the electrical installation is safe and code-compliant: correct conductor size, correct overcurrent protection, approved equipment, proper disconnecting means, bonding, support, and weather-rated outdoor work.

If the AC trip appears alongside other appliance trips, compare the pattern with similar motor and heating loads such as a dryer breaker tripping, an EV charger breaker tripping, or a pool pump breaker tripping. The equipment differs, but the diagnostic question is the same: is the load faulty, is the circuit wrong, or is the panel out of capacity?

The repair depends on whether the fault is in the AC, the circuit, or the service capacity

The right repair is not always a new breaker. A tripping AC breaker is a symptom, and the fix follows the test results.

Possible electrical repairs include:

• Replacing a weak or damaged breaker with the correct listed breaker.
• Tightening or repairing loose terminations in the panel, disconnect, or condenser whip.
• Replacing damaged outdoor conduit, fittings, or conductors.
• Installing the properly sized dedicated circuit for the condenser.
• Correcting an oversized or undersized breaker that does not match the AC nameplate.
• Adding panel space or performing a service load calculation before new large loads are added.
• Coordinating an ESA notification and inspection for new or altered wiring.

Possible HVAC repairs include:

• Replacing a failed capacitor, contactor, condenser fan motor, or compressor component.
• Cleaning the condenser coil and restoring airflow.
• Correcting refrigerant or mechanical issues that make the compressor work too hard.
• Replacing an aging condenser that has an internal short or locked compressor.

The biggest red flag is a breaker that trips repeatedly after reset. That means the protective device is seeing a condition it is not willing to carry. It may be saving the compressor, the wiring, or the house. Leave it off, note the trip pattern, and have the electrical supply and AC equipment checked in the right order.

If the electrical side needs a new branch circuit, start with dedicated circuits for appliances and equipment. For broader troubleshooting topics, the electrical answers hub has related breaker and appliance guides.