How to Keep Your Window AC from Freezing Up

air conditioner unit in a window
  • 1-2 hours
  • Beginner
  • 75-150
What You'll Need
Air compressor
Soap and water
What You'll Need
Air compressor
Soap and water

In the summer months, an air conditioner unit sitting in your window can make life a little more bearable. But as great as these types of units are, they do not come without their own set of problems, such as the AC freezing up in the winter.

Aside from running up your electric bill in the summer, a window air conditioner has also been known to form ice on the vents or freeze up altogether. Some people will attribute this problem to having too much refrigerant in the air conditioner or running it continuously.

Here are a few reasons why your window air conditioner might freeze up and what to do when your AC unit freezes up.

Why Does My AC Unit Freeze?

An air conditioner has a closed loop of coils filled with refrigerant gas. It expands to cool down before pumping warm air outdoors. If air is not circulating, it will not work.

If air is not flowing correctly, moisture in the air can freeze up in the unit. Your AC unit can also freeze up if the drain system isn't working correctly. If it is not, moisture can condense on the coils, which can be a huge issue for the ability of your machine to work correctly.

If the thermostat and fan settings are off, it can also cause freezing.

A low level of refrigerant can also cause freezing in your machine.

Below are a few steps you can take to make sure your AC unit does not freeze up even during the cold winter months. And if your unit does freeze up, fret not, there are a few things you can do to deal with the unit and save it, so it's useful come those hot summer months.

Still, it is better to make sure freezing doesn't happen rather than deal with freezing as it occurs. This will ensure your AC unit has a long life and does not need an expensive visit from a handyman or woman, or even worse, to be replaced.

Make sure you test the machine out when gets warm outside. Do not wait for the hottest day of the year to discover that your window AC unit is not working.

Step 1 - Purchase the Right Size Air Conditioner

One of the most common problems associated with window air conditioners freezing up is that they are either not big enough for the room, or are too big for the room. Either extreme sizing issue will cause ice to form on the vents.

A unit that is too small will have to run much harder than it should in order to keep a large room cooled down. This will result in a lot of condensation forming and resulting in ice.

On the other side of that, an air conditioner that is too large will eventually form ice on the vents because it does not run enough. Condensation from sitting in the sun will form on the coils and condenser.

When purchasing your window air conditioner, make sure it is the right size for the room it will be cooling to prevent it from freezing up.

Step 2 - Check Filter and Change

A routine check of the air filter in the unit will help to prevent you from having any issues. A clogged or dirty filter can cause it to malfunction by not getting an adequate flow of air. Keep the filter clean by removing it and cleaning it with a vacuum, air compressor, or soap and water.

This should be done every couple of weeks during the middle of summer, or when there is an abundance of dust or pollen.

Step 3 - Clean Cooling Coil

During the use of the window air conditioner unit, you might see some condensation forming on the cooling coil. If it begins to turn to freeze up, it means that it needs to be cleaned out. This is a job for a professional cleaner because it needs to be flushed out, but you should always keep your eye on this.

This should be cleaned regularly, every one to two years.

Step 4 - Do Not Run in Cold Temperatures

When the temperatures outside begin to drop, the temperature in the cooling coil will also drop. This, coupled with the rising moisture and heat from the house, will cause the unit to freeze up.

Once the evenings begin to cool off and the daytime temperatures are comfortable, you should remove the unit from your window, so it doesn't cause frost and ruin it.

Dealing with a Frozen Unit

A window air conditioner is a good option if you are looking to cool a small room or office. Window air conditioners save you from the higher costs involved with installing a central air conditioning system. In fact, in many countries all over the world, window air conditioners are the preferred method of cooling in summer.

Although window air conditioners offer a number of advantages, they also have some disadvantages. One of the biggest problems associated with these air conditioners is the accumulation of ice outside the air conditioner unit. In particular, this problem is prevalent in colder weather.

While most air conditioners see their heaviest use during the hot summer months, it is still possible for a central or window air conditioning unit to freeze up during these months, especially if you did not do the steps above. If you find that your unit has frozen, you will need to deal with it immediately.

Unfortunately, the solution isn’t quite as simple as just physically removing the ice in your AC system. To do so is treating the symptom and not the underlying cause, and it probably won’t permanently unfreeze your unit.

There are a variety of causes of this problem, all of which will dictate how you go about solving it. However, before you even begin to diagnose or repair the problem, the first thing you have to do is thaw the ice.

window AC covered in snow

Step 1 - Check Outside Temperature

While window air conditioners can cool a room very effectively when it’s hot, unlike central air conditioning, these units are not really designed to work in very cold temperatures. During the process of cooling a room, it is natural for condensation to trickle down from the outside of a window air conditioning unit.

If the temperatures are low, the condensate can freeze and lead to ice formation on your window air conditioner. Since most window air conditioners do not have a heating function, it doesn’t make sense to run them when the temperatures drop.

Step 2 - Thaw Ice From an Air Conditioner

Switch off the air conditioner and disconnect the electrical supply. You will need to deactivate the breakers, so the circuits do not short out during the thawing process.

WARNING: This is a very important step. The unit must be off and its breakers as well. Water and electrical appliances do not mix.

Use a hair dryer to thaw out the ice, and then use a cleaning rag to wipe off the moisture. Of course, if your window air conditioner is located in a room that is not on the ground floor, it could be dangerous to try to clean it from the outside.

Under such circumstances, switch off the air conditioner and allow the ice to melt naturally from the heat of the sun.

As the air conditioner thaws, water will drip and leak from the unit itself. To prevent the thawing water from creating a mess, fix a trash bag or bucket underneath the air conditioner unit. Monitor this carefully over the next couple of hours as the ice melts.

Once the ice has melted, allow the air conditioner unit to dry for 24 hours. Ensure the unit is entirely dry before operating it again.

Step 3 - Determine the Underlying Cause of the Freezing

There are several potential causes of freezing in an air conditioner unit. The filters, cooling coils, and fins may all be completely or partially responsible. In order to ensure your air conditioner does not continue to freeze in the future, examine each of these component pieces for maintenance needs.

Step 4 - Check and Clean the AC Filters

window AC with dirty filter

Filters that are worn out or dirty may contribute to freezing in an air conditioner. Check to see if the filters are broken or need to be replaced. Typically, you should plan on cleaning or replacing the filters in your air conditioner unit every two to three months. Test them to ensure air can flow through them with ease.

The filter is one of the few parts of a window air conditioner that can and should be cleaned on a regular basis. Unfortunately, this is often overlooked. Over time, the filter becomes clogged, and this reduces the airflow. This not only reduces the efficiency of the air conditioner but can also result in ice formation.

Switch off the air conditioner and unplug it from the electrical supply. Open the front grille and remove the filter. This is a rectangular mesh-like unit made up of a foam-like material. Use a vacuum cleaner or hand brush to remove the excess dirt, and then rinse the filter with water.

Allow it to dry and then refit it. Switch on the air conditioner. You should notice a marked improvement in its efficiency. Many new window air conditioner units come with an indicator that shows when it is time to clean the filter.

Step 5 - Check Cooling Coil

The cooling coils in the air conditioner unit, also known as evaporator coils, are also potential contributors to freezing units. Essentially, the coil evaporates heat from the inside of the unit to the outside of the air conditioner system.

By removing this heat, the coil lowers its temperature, and in conjunction with your AC’s coolant, this is the component that actually gets cold and allows your system to blow cool air.

Because of either poor airflow within the unit, which can stem from the filter problem mentioned above, or a lack of coolant, the evaporator coil can overcool itself to the point of creating condensation, which eventually freezes into the ice.

To treat the cooling coils, clean any dirt off of them carefully. As you do this, be careful not to bend any of the cooling fins that are attached.

Step 6 - Check Cooling Fins

AC cooling fins

The cooling fins work in harmony with the evaporator coil. The fins are electric or mechanical. They are just physical structures that increase surface area for heat transfer within the unit.

In the case of an air conditioner, the fins provide more surface area for heat to travel along and it moves away from the cooling coil and out of the unit and into the atmosphere. Assuming the fins aren’t broken, the best way to treat them is to use a vacuum cleaner to thoroughly clean the fins.

Examine the air conditioner fans to ensure they are working properly as well.

Step 7 - Evaluate Problems with the Air Conditioner’s Coolant

If you’ve ruled out other potential causes, it may be time to test the coolant levels, as this is a frequent cause of air conditioner freezing.

Unfortunately, many local regulations will not let an individual deal with refrigerant, and it may be necessary to contact a professional maintenance person or air conditioner technician to test and replace the coolant in your air conditioner.

However, you can test and replace your air conditioner's Freon on your own, assuming local regulations allow it.

If any of these component pieces of the air conditioner do not seem to be functioning adequately, investigate whether they may be maintained at home or whether it is beneficial to hire an air conditioner technician. Thoroughly examining and maintaining your conditioner will decrease the chances of repeat freeze-ups in the future.


By following the steps outlined above, you can prevent your window AC unit from freezing up or help save it once it has.