Window Air Conditioner Freezing Up? 8 Common Causes & Solutions

Window air conditioners, like other types of air conditioners, can freeze at times. Many people are unsure what is wrong or how to deal with it.

In fact, there are many reasons for a window air conditioner to freeze up, including a dirty filter, a filthy evaporator coil, low outdoor temperature, and a refrigerant leak. Accordingly, you can’t address it in the same way.

In this post, I’ve summarized 9 common causes and solutions so you can troubleshoot them one by one. Some problems can be fixed easily on your own. 

It is dangerous to leave a frozen window ac unattended! You must fix it as soon as possible.

Damaging effects of a frozen window air conditioner

Since I’ve already mentioned how important it is to fix a frozen window air conditioner, let’s begin this post by illustrating the potential consequences.

Once the window air conditioner freezes up, its compressor, fan, and other components need to work harder to keep the same room temperature. The refrigerant may not be able to be kept in gas form when it enters the compressor.

This will lead to overheating and damage to the whole air conditioning system. Accordingly, the lifespan will be deducted, and you will need to pay more for electricity bills and repair services.

Therefore, you should pinpoint the cause of freezing up and fix it as soon as possible.

How to unfreeze a window ac?

Before looking for the cause, you need to unfreeze your window ac. The ice is located in the evaporator coil, and your best bet is to allow it to thaw naturally. Unplug the cord and wait for a while until the ice is melted and drains away outside the house. 

Don’t try to speed up the process by pouring hot water or using other tools.

What causes a window AC unit to ice up? [Solutions included]

Once all the ice is melted, you can start to diagnose the problem. As I mentioned, many reasons can cause a window AC to freeze. You can write down all the possible causes in this section and rule them out one by one. 

1. Dirty air filter 

A window air conditioner uses refrigerant to cool the indoor air. When the refrigerant passes through the evaporator coil, it can absorb heat from the air and then release it outside when compressed.

When the air temperature falls below the dew point, the excess moisture in the air condenses and falls into the drain pan.

When there is insufficient air to warm up the coil, the refrigerant begins to turn the water particles left on the coil to ice.

The air filter is located in front of the evaporator coil and is responsible for filtering out contaminants in the air. However, it can become clogged over time as more dust, dirt, mold spores, or other particles accumulate.

The airflow will be reduced, allowing less air to pass through the evaporator coil and causing it to freeze.


Easy peasy! Turn your machine off and remove the filter. Rinse it under running water with a brush and allow it to dry before replacing it.

2. Filthy evaporator coil 

Aside from the air filter, airborne particles can accumulate on the evaporator coil. This will obstruct the refrigerant’s heat absorption, causing it to absorb heat from water particles rather than air.

When water particles lose heat, they freeze, which is why you see frozen evaporator coils.


To access the coils, move the window ac to a flat surface and remove the front cover. Remove the surface grime with a vacuum or brush, then apply the coil cleaner to dissolve the stubborn buildup.

If necessary, rinse the coils with water and let them air dry.

3. The fan speed is too low

The fan speed decides how much airflow you can get in a certain period. If the fan speed is too low, the airflow will be limited, causing your window ac to freeze. 

Sometimes, it is because you set the fan speed too low. If not, there may be something wrong with the fan or the fan motor. The fan may get loose, or the motor may be damaged.


To increase the fan speed, change the setting. If the fan speed does not increase, remove the fan and reset it to tighten the fan or replace the fan motor.

4. Refrigerant leak 

In most cases, the refrigerant will remain untouched in the coils and compressor. However, refrigerant can leak out due to wear and tear.

When the refrigerant level drops, the refrigerant gas expands, allowing it to absorb more heat. That is, the coils will become colder and more ice will form on them.


You are not allowed to recharge the window ac. You need to ask a certified HVAC expert to seal the leak and recharge your ac. 

5. Defective compressor 

When the compressor fails, the ac continues to operate at a low efficiency, causing the refrigerant to absorb more heat. As a result, the coil will eventually ice up.


A compressor is very expensive to replace or repair. Buying a new window air conditioner is usually the better option.

6. Clogged drain hose

This is a cause of a window ac freezing up that is often neglected. When the drain hose is blocked, more moisture will remain on the coil, increasing the likelihood of freezing up.


The drain hose of a window air conditioner is detachable. You can remove it and use a long brush to dislodge the slime in the hose. You can replace it with a new hose if it is too hard to access.

7. Outdoor temperature is too low

outdoor temperature too low

Air conditioners can’t work properly when it is cold outside. This is because the air is already so cold that it is not able to provide enough heat for the refrigerant to absorb. As a result, the window ac unit will freeze up.


Don’t use your window ac when the temperature is below 60 degrees. 

8. Your window unit is oversized

When your window ac unit is too large for your room, it will quickly lower the temperature and shut off. It will turn back on once the temperature in the room rises slightly. That’s why it turns on and off repeatedly

Under this circumstance, the evaporator coil will become excessively cold, which leads to icing.


Unfortunately, you must consult with an HVAC company to determine the size of window ac required for your room and then purchase a smaller model.

9. Wiring problem

If none of the solutions work, you should investigate whether there is a wiring problem in the electrical components.

For example, if the connection to the temperature sensor becomes loose, the machine may continue to operate even if the room temperature reaches the desired level and the coil becomes too cold.


If you don’t have the expertise, you will need the help of a certified electrician.

Prevent your window AC from freezing up

The best way to keep your window air conditioner from freezing is to clean and maintain it on a regular basis. It is recommended that the filter be cleaned once a month and the coils and fan be cleaned twice a year.

As a result, your device will have better airflow and will be less likely to freeze.

Check here if other types of air conditioners in your house also freeze up.

About The Author

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Liz Yang is the founder of Airsmartly. She has been working at home for a few years and realizes that the performance of the HVAC system plays such an important role in our life. She has tested dozens of products in person, like humidifiers, air purifiers, dehumidifiers, and ACs, and wants to share tips about using or troubleshooting these products with you. Her uncle is an HVAC expert with over 30 years of experience in the field, and often offers assistance when she is unsure how to handle a situation. He is also in charge of reviewing the articles on this site.

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