Why Won’t My Window AC Unit Turn On?

Window air conditioners are rather simple appliances that cool you off. If yours isn't working, there is usually an easy explanation. Don't sweat it.

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In the heat and humidity of summer, many of us seek relief with air conditioning. For those without central air conditioning, a window air conditioner can help bring down the temperature. But what happens if your window air conditioner won’t turn on? We’ve found the most common failures that cause this problem, some of which are easy to fix yourself.

Reasons Your Window AC Won’t Work

Power Problems

While a central air system is hard-wired into your home’s electrical panel, a window air conditioner typically plugs into a wall outlet somewhere near the window. If it won’t turn on, your first step should be to check to make sure it’s plugged in and that the power cord isn’t damaged. Brandi Andrews, CEO of National Air Warehouse, says she’s seen many power cords chewed by rodents — a problem that may not only cause the machine to suddenly stop, but can create a fire hazard as well.

Another possibility: Your circuit breaker could be overloaded and tripped, cutting power to the window air conditioner. Here’s how to reset it. Be sure to double-check the rating plate on the air conditioner for the amperage required, to ensure that your breaker can supply the proper current.

Chris Forbus, owner of Choice Air Care in Frisco, Tex., says that using an extension cord can also increase the load on the circuit, causing the circuit breaker to trip. Don’t use an extension cord with a window air conditioner. While there are some specialty, heavy-duty extension cords labeled for use with window air conditioners (usually with 10-gauge wire meant to handle the higher amperage draw), the experts we spoke with suggest that these be only used temporarily.

Dirty Fins and Coils

Your window air conditioner is a machine, and like all machines it requires maintenance. Be sure to clean the coils and cooling fins through which refrigerants flow, which are narrow and tend to trap dust and debris. If the cooling fins or filters are dirty, the insufficient airflow can cause the unit to not turn on.

Oscar Aparicio, a heating and cooling instructor at San Joaquin Valley College, says that skipping this maintenance step can doom an air conditioning unit. “A dirty coil can lead to multiple failures, including high head pressure, which overworks the compressor,” he says. That creates insufficient airflow, leading to inadequate cooling and higher electricity bills.

Also, be sure to change air filters. This will also extend the time between coil cleanings, thanks to less dirty air making it through the machine.

Leaking or Low Refrigerant Charge

Your window air conditioner’s refrigerant is meant to be in a closed system because refrigerants can be harmful to the environment. One sign of leaking or low refrigerant is ice on the air conditioner coils. This means the coil can’t properly disperse the heat, so condensation freezes. If the ice is bad enough, your air conditioner might not start.

If you suspect a refrigerant leak, don’t try and troubleshoot this yourself. Instead, search for a specialist with an Environmental Protection Agency (EPA) refrigerant repair certification who can safely trace and repair leaks. Often, however, new window air conditioners are priced reasonably enough that it may be cheaper to buy a new one than pay for repairs. Here are some tips on getting rid of old appliances.

What If My Window AC Won’t Turn Off?

Your window air conditioner unit temperature is regulated by a thermistor or a thermostat. These sensors can occasionally fail. When they do, the air conditioner can’t read the temperature in the room, so it may continue running even after the set temperature has been reached.

Depending on the model, the thermostat or thermistor can be checked for continuity. If it doesn’t have continuity when the air conditioner is trying to cool, replace the thermostat or thermistor if possible. On some models, the thermistor or thermostat is part of the main control board and can’t be removed.

Chris Tonn
A lifelong Ohioan, Chris grew up around classic rusty sports cars from Japan and England. He's been covering the automotive industry for nearly 10 years, and is a member of the Midwest Automotive Media Association (MAMA). A family man, Chris drives a Chrysler minivan, and uses his rusty old Miata as a shelf, until the day it is uncovered as a priceless barn find.