Window Air Conditioner Keeps Tripping the Breaker? Causes and Fixes

A window air conditioner usually trips the breaker because the circuit is overloaded, the plug or cord is poor, or the unit is working too hard. Plug it straight into a wall outlet, move other devices off that circuit and clean the filter. If it still trips alone, the start capacitor or compressor may be failing and the unit needs service.

A breaker that trips on a hot afternoon is protecting the wiring in your walls. This guide covers the causes in the order that is easiest to check, from free fixes to the signs that mean you should stop.

Why does my window AC keep tripping the breaker?

The most common reasons are these:

• Too much on the circuit. A window unit can draw a large share of a standard 15 A circuit. Add a TV, a space heater or a second AC in the next room, and the total passes the limit.
• A dirty filter or coils. Restricted airflow makes the fan and compressor work harder, which raises the current the unit draws.
• A loose plug or worn outlet. A poor connection creates resistance and heat. Some units have a built-in safety plug (a LCDI or similar) that trips if it senses a fault in the cord.
• A failing start capacitor. The capacitor helps the compressor and fan motor start. When it weakens, the motor stalls and pulls too much current.
• A frozen evaporator coil. Ice on the coil, often caused by a dirty filter or low outdoor temperatures, strains the unit.
• A shorted or failing compressor. This is the serious one. It usually trips the breaker every time, within seconds of starting.

What the pattern tells you

How to fix it

1. Turn the AC off and unplug it. Reset the breaker. If it trips again with nothing plugged in, the problem is in the wiring or the breaker, so call an electrician.
2. Plug the AC straight into a wall outlet. No extension cord, no power strip, no multi-plug adapter.
3. Take other loads off that circuit. Turn off or unplug heaters, hair dryers, microwaves and big TVs on the same circuit. To find out what shares it, switch the breaker off and see what loses power.
4. Clean the filter. Slide it out, wash a reusable mesh filter in warm soapy water, let it dry and put it back. Do this every couple of weeks during heavy use.
5. Check for ice. If the front coil is frosty, turn the unit to fan only until it melts, then clean the filter before using cool mode again.
6. Inspect the plug and cord. Look for scorching, a hot plug or a cord that is cracked or kinked. Do not use a unit with a damaged cord.
7. Let it rest between runs. If you turn the AC off, wait three to five minutes before turning it on again.
8. Try a different circuit. If it runs fine on another circuit, the first circuit is overloaded or has a wiring or breaker problem.

Is the unit too big for the circuit?

Window units are rated in BTU. Smaller units (roughly 5,000 to 8,000 BTU) usually run on a standard 120 V household circuit without trouble. Larger units draw more current and some are built for a 20 A circuit or a 240 V outlet. Check the label on the side or back of the unit for its amp rating and the manufacturer's note on the circuit it needs. If the label calls for a dedicated circuit, other devices should not share it.

An electrician can add a dedicated circuit, which is the cleanest fix for a big unit in an older house.

The capacitor and compressor

If you have tried everything above and the unit still trips within seconds of the compressor starting, the likely culprits are the start capacitor or the compressor. A bulging or leaking capacitor is a clear sign, but testing and replacing one means opening the unit, and a capacitor can hold a charge even when unplugged. That job is for a technician.

Window units are often cheap to replace compared with a compressor repair. Ask for a quote, then compare it with the price of a new unit of the same size, especially if yours is more than 8 to 10 years old.

When to call a professional

Call a licensed electrician or an HVAC technician if:

• The breaker trips immediately every time, even with the AC alone on the circuit.
• The outlet, plug or wall plate is hot, discolored or smells of burning.
• The breaker will not reset, or trips with nothing plugged in.
• You need to add a dedicated circuit for a larger unit.

What not to do

• Do not use an extension cord or a power strip.
• Do not keep resetting a breaker that trips at once.
• Do not run two window units on one 15 A circuit.
• Do not open the unit while it is plugged in.

Bottom line

Start with the easy checks: wall outlet, a lighter circuit and a clean filter. If the unit trips on its own on every circuit, treat it as a failing capacitor or compressor and decide between repair and replacement. If your home still feels sticky with the AC running, read a house that feels sticky even with the AC running. Other heavy appliances can overload a circuit in the same way, as in a space heater that trips the breaker.