How to Troubleshoot and Repair Your Window AC Unit

man repairing window AC
  • 1-2 hours
  • Intermediate
  • 15-30
What You'll Need
Rubber gloves
Fuse wires
Voltage tester
What You'll Need
Rubber gloves
Fuse wires
Voltage tester

The sweltering dog days of summer arrive every year, putting a strain on millions of window-mounted air conditioners. For many, these window units are their only way of cooling off their homes, and thus their ability to function correctly is essential. But the unfortunate truth is that sometimes they break down for one reason or another. With your AC not working, things can get uncomfortable fast. Check out our tips for window AC repair below.

Air Conditioner Troubleshooting

If your AC won't turn on, the problem could be in one of many parts. Troubleshooting air conditioners is a process of elimination to find the faulty element.

Fan and Blower

The fan cools the compressor coils by blowing outside air against them. Meanwhile, the blower, placed on the other side of the fan, pulls hot air from the room over the evaporator coils to cool it before recirculating it back into the room.

These fans and blowers can often get clogged and need to be cleaned.


window AC filter

The filter is a thin, pleated screen that keeps dirt and debris out of the air conditioner's internal components and cleans the air before it's recirculated back into the room.

The filter will be placed either inside or behind the face panel, a plastic or metal cover on the front of your air conditioner that must be removed first to access the air conditioner's components.

This panel may be held in place by screws, tabs, clips, or both depending on the unit. Filters are one of the easiest ways to fix an AC window unit as they are frequently clogged and thus need to be cleaned or replaced.


This device, usually a tiny copper tube of three to four inches in length, monitors the room temperature and controls the air conditioners on/off cycle. It's usually attached to the front of the evaporator.

Thermostats may occasionally break or fail, meaning they can no longer take an accurate temperature reading. This may cause your window unit not to turn on or run constantly.


The compressor compresses the refrigerant into a hot and cold liquid for the condenser and evaporator. An internal motor drives the compressor, usually situated between the evaporator and the condenser (compressor motor).

Condenser Coils

The condenser, located near the back of the unit, has the same components as the evaporator (copper tubing, fins, and refrigerant), but it absorbs hot air from the room blows it outside via a fan (the condenser fan).

Evaporator Coils

The evaporator is made out of copper tubing (evaporator coil) wrapped by thin aluminum fins and is located right beneath the filter. The refrigerant in the evaporator coil converts and cools the heated air to cooler temperatures.

Chemical Refrigerant

To catch and cool off hot air, a liquid (in the condenser) or gaseous (in the evaporator) compound passes between the air conditioner's evaporator and condenser coils.

A lack of refrigerant will cause the air coming into the window unit not to be cooled, meaning you won't get the cold air you need.


This cylindrical device holds an electrical charge that allows the compressor and fans motor to start and run. Two electrical contacts emerge from the top of the cylinder and connect to the compressor and fan motor.

How to Fix AC (First Steps)

man repairing window AC

Proper Installation of Your AC Unit

The correct installation of your AC unit may be the first step to figuring out and solving everyday problems with a window unit not working or blowing cool enough air.

Check and make sure that your window unit is installed correctly by making sure that it is well fitted into the window, that the side panels fit correctly, and that there is enough space inside and outside for proper airflow.

Remember, not having enough space outside the window can impede airflow, such as in between bushes or close to a tree. This lack of airflow means less cool air coming in.

Additionally, window units work best when in a semi-shaded area rather than in full view of the sun, where they have to work harder to cool off the super heated air from outside.

Correct Sizing

Not all window air conditioners are created equal. The cooling power of a window air conditioner is measured in BTUs or British Thermal Units, and some window units will have higher capacity BTUs than others.

If you wish to cool off a square foot of space, most window air conditioners require 20 BTU, meaning that if you want to cool a 500-square-foot room with an average ceiling height, you'll need a 10,000 BTU window air conditioner.

If you think your window air conditioner is damaged because it is not cooling off the room well enough, check the BTU rating to discover how much cooling power it has.

You could just be cooling your home with an air conditioner that is too tiny. If this is the case, you have two options: upgrade and replace your current window air conditioner with one with a larger BTU rating, or invest in a second unit to function in tandem with your current one.

Cleaning Your AC Window Unit

washing AC unit

Another easy fix for many AC window units not running or not pushing out cold air is to clean them. AC window units often get clogged with dirt and debris, either in the filter or internal mechanisms, so a good cleaning might be enough to get it back into working shape.

To clean your air conditioner thoroughly, you'll need a few items that you can find readily around your house. Gather these necessary supplies before you begin:

  • Warm or hot water
  • Detergent or mild soap
  • Disposable cloth
  • Spray bottle filled with three percent hydrogen peroxide
  • Soft-bristle brush or fin comb
  • Pressurized air
  • Screwdriver

The most important thing you can do to maintain your window AC unit running correctly is clean the filter. Even if you don't clean the entire appliance, it's good to wash the filter monthly and change it regularly.

Depending on environmental circumstances, filters may need to be replaced every six weeks to six months.

Ensure that you have turned off your AC before removing the front panel and filter. Use a vacuum to remove as much dirt, dust, and hair as possible.

After that, wash your filter in warm, soapy water and air dry it. Wait until it's completely dry before reinstalling it in your window air conditioner.

After that, vacuum the evaporator and condenser. Spray both devices with compressed air or an air conditioner coil cleaner for a more thorough clean. You should also use a knife or fin comb to straighten any bent evaporator or condenser fins at this time.

Finally, replace everything, including the filter and front panel, then turn everything back on and see if this fixed your cooling issues.

How to Fix a Window Air Conditioner That Isn't Cooling

window AC filter

Window air conditioners are relatively simple cooling devices. If yours isn't working, there's generally a simple reason. Don't be concerned; simply follow this guide to ensure that everything is in working order and follow a few easy steps to repair them if issues arise.

Window AC Unit Won't Turn On

A window air conditioner typically plugs into a nearby wall socket. Check to see if it's properly plugged in and that the power cable isn't damaged if it won't turn on.

Animals may chew on interior wires occasionally, or a person tripping over the cord may cause damage, ensuring that power is no longer reaching the AC.

Another possibility is that your circuit breaker has tripped due to overload, stopping power to your window air conditioner. Double-check the amperage required on the air conditioner's rating plate to ensure that your breaker can give the necessary electricity.

When used with an AC window unit, an extension cord can also increase the load on the circuit and cause the circuit breaker to trip and thus should not be in use.

Window AC Not Blowing Cold Air

One of the most crucial components of any air conditioner is the compressor. It circulates the refrigerant, traps the heat from the heat inside your home, and discharges it outside, like a pump.

This circulation allows cold air to flow, and the air conditioner will not work correctly without a properly operating compressor.

If your AC is producing warm air, even in Cool Mode, the filter and fins are clean, and there are no other apparent problems with the unit, it could be a sign that your compressor has failed.

It's probably time to replace your window air conditioner if your compressor has failed. Because the compressor is a costly component to replace, investing in a new window air conditioner is likely more cost-effective.

AC Window Unit Leaking or Freezing Up

Low or leaking refrigerant could cause your AC window unit's fan to function but with no cool air. Ice appearing or coolant bubbling on the air conditioner coils is one symptom of refrigerant leakage or low levels.

Because refrigerants can damage the environment, your window air conditioner's refrigerant should be in a closed system, so cracks or leaks are something that should grab your attention.

If you suspect a refrigerant leak, don't attempt to fix it yourself. Instead, get a professional to fix the leak or buy a new unit. Many are fairly priced nowadays and may be less expensive than employing an expert.

AC Window Unit Constantly Running

A thermometer in window air conditioners monitors the area's temperature to be cooled and might be one reason your AC is constantly running or refusing to turn on. It sends signals to the compressor to switch on or off the cold air based on the surrounding temperature.

The thermometer will transmit a signal to the compressor to turn off the cool air once the area has reached the required temperature or keep blasting the cold air if the area is still too hot.

To find the thermostat in your window air conditioner, remove the exterior shell and reveal the electrical control board. The thermometer is a little copper tube situated on or near the control board once you've found it.

Examine your thermometer for signs of wear and tear, paying close attention to any disconnection or damage. You should replace it if it shows symptoms of wear.

You can change it yourself, but use a new thermometer that the manufacturer has approved for your window air conditioner! If you don't feel comfortable changing it yourself, you can hire an expert.

Window AC Unit Really Loud

No one likes to hear their window unit starting its rock and roll band. So why is it suddenly rattling and making a loud noise? A straightforward problem might be that a foreign object has fallen into it.

Leaves and other debris can fall into the slats on the outside, whipping around inside, hitting the fan and sides and making loud noises.

Additionally, you might also have damaged fan blades, causing them to bend and creating loud noises. Lack of lubrication can cause loud squeaks or grinding noises, so simply greasing the gears (which can occasionally be hard to reach) can fix that.

And finally, check to see how well the unit is seated in the window. Rattling and popping noises might be coming from the unit itself shaking in its setting, which can be easily rectified by ensuring it is properly positioned.

Wrap Up

We hope this article has helped with some AC troubleshooting when it comes to why your window air conditioner unit is not working. You can perform many of these simple solutions by yourself in your own home, but, as always, reach out to a professional for more help.

Check out our blog for more window unit topics such as performing seasonal maintenance or how to remove bad smells from your unit.