Window AC Not Cooling? Here’s What to Do

Did your window AC suddenly stop cooling? Hot temperatures in your home can become unbearable pretty quickly. 

So how do you fix your window AC? It could be due to many things.

In this article, I’ll go over all the reasons why your window AC isn’t cooling. I’ll also let you know what you need to do to fix your window AC and get your room cool again!

Check window AC’s thermostat and mode settings

Your window AC won’t cool your room if its thermostat is not set properly. The temperature setting on the thermostat must be set to a lower temperature than your room’s temperature.

For example, if your room is 80°F then you could set the thermostat to 72°F. Setting the thermostat to a lower temperature lets the AC know that it needs to cool your space.

Another thing to check is the mode settings on the window AC. Most window ACs nowadays have many different settings:

  • Cool mode
  • Auto mode
  • Fan-only mode
  • Dehumidify/dry mode
  • Heat mode (if available)

Depending on the specific model of your window AC, you may have one or more of these settings.

Cool mode

If you need your window AC to cool your room, be sure that it is set to cool mode.

When your window AC is in cool mode, it knows that your intent is to cool your room. Your window AC will cool your room until it reaches the temperature that you set on the thermostat.

Auto mode

If you need your window AC to cool your room efficiently, then auto mode is a good option as well.

When your window AC is in auto mode, it will find the best settings to maintain your room at whatever temperature you set on the thermostat. When in auto mode, the window AC will cycle on and off and adjust its fan speed to deliver the right amount of cooling for the situation.

Fan-only mode

When your window AC is in fan-only mode, the fan will run but the AC will not cool your room.

Fan-only mode is useful if you just need to circulate the air in your room or use your window AC like a ceiling fan.

There’s also a trick to using fan-only mode when it’s cool outside. Some window ACs have vents that let fresh outside air in. If you open the outside air vent and turn on fan-only mode, you can get fresh, cool air from outside into your room. This is perfect for autumn when it’s cool outside, but you still need AC indoors.

Dehumidify/dry mode

Dehumidify mode or dry mode will make your window AC function as a dehumidifier.

Most window ACs with heat have this mode. When dehumidify mode is enabled, your window AC won’t cool your room. Instead, it will blow out dry room-temperature air.

Dehumidify mode works by cooling your room’s air to rid it of moisture, then reheating the air. The result is dry, room temperature air blown out of your window AC.

Even if your window AC doesn’t have heating, it still might have a dehumidify mode. In this case, the window AC will cool the air at a low fan speed. This will cool your room, but not as much as the AC normally would since its main goal is to dehumidify your room.

Heat mode

Many window ACs on the market nowadays have heat mode. Heat mode works by running an electrical current through a heating coil. The AC’s fan blows air through the heating coil to deliver the heat to your room.

A window AC’s heat mode is no different than an electric space heater. The drawback is that electric heating is usually the most expensive way to heat your home.

So if you have other ways to heat your room (such as central heating) then I recommend using that instead. However, if you just need a short-term solution to heat a small space, then a window AC’s heat mode will work just fine.

Check the window AC’s air filter

Did you know that your window AC has an air filter? Many people don’t!

A dirty air filter is one of the top reasons why a window AC isn’t cooling. The air filter needs to be cleaned every so often. Even more so if you have a dusty home or pets running around.

When your window AC’s air filter is dirty, it inhibits airflow through your window AC. Your window AC will have to work harder to cool your room. If your filter is clogged, your AC may struggle to keep your room at a stable temperature.

To clean your window AC’s air filter, open the filter access panel on the front of the AC and remove the air filter. The filter access panel is the large plastic grille on the front of the window AC.

Next, spray the air filter with water. Spray the backside of the air filter, that way the dust gets blown out through the front of the filter.

If your air filter is really dirty, then you can use a soapy water solution to clean the excess grime off the filter. You can also use a toothbrush to scrub the nooks and crannies on the filter.

After you’re done cleaning the air filter, rinse it out with water and set it out to dry. Allow the filter to completely dry before reinstalling it into the AC.

Clean the window AC air filter

Window AC is not cooling but the fan is running

Is your window AC blowing air around your room but not cooling it? It could be due to a basic problem, like an incorrect setting. Or it could be due to a broken component in the AC.

If your window ACs fan is running but not cooling your room, then it is likely one of these things that are causing it:

The mode setting on the window AC is wrong

The window AC’s mode setting determines how the window AC behaves. If your window AC is in the wrong mode setting, then it won’t cool your room.

Put your window AC in cool or auto mode to get cooling. You also need to turn the window AC’s thermostat temperature down to get cooling.

There is a compressor or refrigerant issue in the window AC

The compressor is the heart of the cooling system in an AC. If the compressor isn’t working, then your window AC won’t cool. A broken compressor could be caused by many different things, all of which are outside the realm of DIY fixes.

A refrigerant leak is another possible cause of a non-cooling window AC. The refrigerant is the fluid that transfers heat through the AC. If the refrigerant leaks out of your window AC, then your window AC won’t be able to cool your room.

If you suspect that your window AC is having compressor or refrigerant issues, then I recommend having an HVAC professional take a look at your unit.

There’s also a chance that the compressor in your window AC is working fine, but the coils need to be cleaned. Read below to find out more.

Window AC is not cooling room enough

If your window AC is blowing out air that’s slightly cold, then its compressor and fan are working fine. The issue is something else.

If your window AC is not cooling your room enough, then it could be due to one of these things:

The evaporator or condenser coil is dirty

The evaporator and condenser coils are the parts of a window AC that transfer heat from the inside of your room to the outside of your home. If one of these coils is dirty, then you’ll have reduced heat transfer and performance from your window AC.

Fortunately, cleaning your window AC’s coils is something that you can do yourself. You don’t even need to remove the AC from the window.

I’ve written a guide on how to clean your window AC without removing it. It details the process of cleaning the evaporator and condenser coils, so I recommend checking that out below.

Your window AC has a refrigerant leak

If your evaporator and condenser coils are clean but your window AC is still not making air that’s cold enough, then your window AC may have a refrigerant leak.

If your window AC has a refrigerant leak, then it will only be able to cool your room at a reduced capacity. Once all the refrigerant leaks out, then your AC won’t cool at all.

Unfortunately, there is no easy way to fix a refrigerant leak in a window AC. You’re better off calling an HVAC professional to diagnose the issue.

Even then, it’s often cheaper to just replace the entire window AC unit instead of paying someone to fix a refrigerant leak.

Your window AC is undersized

An undersized window AC won’t have enough capacity to remove heat effectively. Simply put, your window AC can’t keep up with cooling your room.

In some cases, the AC is too small to begin with. Or maybe it’s just a hot day. Either way, your window AC is working fine if it’s blowing the right amount of cold air for its size.

If your window AC is working correctly but still not cooling your room here are some things to try:

  • Shut windows and doors to prevent warm air from getting into your room
  • Use blinds or curtains to block sunlight from getting into your room
  • Adjust the vents on the window AC to disperse air through your room more effectively
  • Use a fan to circulate the cool air throughout your room

If all that fails, then your window AC might be undersized for your space. Consider replacing your window AC with one that’s slightly bigger to make up for the increased heat load in your space.

Hi, my name is Trey Lewis and I’m the founder and chief editor at HVAC Training Shop. My goal for this website is to help homeowners troubleshoot and maintain their home’s HVAC systems. Whether it’s changing an air filter, troubleshooting a blower motor, or just buying a new humidifier, I want to make sure that you’re covered.

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