Window AC keeps tripping the breaker

Symptoms

• Breaker trips shortly after the unit starts
• Trips more often on hot days
• Lights dim when the unit kicks on
• Trips when other appliances run on the same circuit

Likely causes

• CommonAC sharing a circuit with other high-draw appliancesWindow units draw a large startup surge that can overload a shared circuit.
• CommonDirty coils or filter making the compressor work harderRestricted airflow increases the current the compressor pulls to run.
• PossibleUndersized circuit for the unit's amperageLarger window units often need a dedicated 15–20 amp circuit.
• PossibleWeak or failing capacitorA capacitor that can't smooth the startup surge causes a current spike that trips the breaker.
• Less commonFailing breakerAn old breaker can trip below its rated load even when the AC draws normally.

What to do

1. Unplug everything else from the outlet and circuit the AC uses and try running it alone.
2. Clean the filter and check the outdoor coil for buildup that could be making the compressor work harder.
3. Check the unit's nameplate for its amperage and confirm the circuit and breaker are rated to handle it (many large units need a dedicated 15–20A circuit).
4. Reset the breaker fully off then on, and note whether it trips immediately or after the compressor kicks in.
5. If it trips right when the compressor starts even on a dedicated, clean circuit, suspect a failing capacitor.
6. Avoid repeatedly resetting a breaker that trips instantly, since that can indicate a short.

Tools and parts

• None

When to call a pro

Call a licensed electrician if the breaker trips even with nothing else on the circuit, and an appliance technician if it trips specifically when the compressor kicks in.

Safety