7 Reasons for a Window Air Conditioners Freezing Up

Window air conditioners are becoming increasingly sophisticated, featuring features like scheduling functions and eco modes. These advanced capabilities enable you to personalize your experience with the unit while making it more energy-efficient.

These features are particularly beneficial if you live in an area that gets cold and want to save energy on your power bill. Today’s window air conditioners are much more effective and powerful than the ones we had as children, allowing for greater savings on cooling costs.

1. Dirty Filter

When your air filter becomes dirty, it can reduce the amount of cool air flowing through the blower. This causes your fan motor to work harder and uses up more energy, increasing energy use for your air conditioner.

Your air filter can also prevent cold air from passing through your evaporator coil (cooling coil). Without sufficient circulation, condensation builds up inside the coil and freezes, hindering its ability to operate effectively.

Regularly replacing your air filter is a cost-effective and simple way to improve the indoor air quality in your home. Furthermore, having a clean filter helps your system run more efficiently, saving money on energy bills in the process!

Although there could be several reasons why your window air conditioner might be freezing up, a common culprit is likely due to an unclean filter. If you’re still worried, here’s what you can do: make sure the filter is clear or replace it if clogged with dirt.

Window Air Conditioners
Window Air Conditioners

2. Dirty Evaporator Coil

Your evaporator coil can become dirty if it cannot absorb as much heat from the air in your home, forcing your AC to work harder than necessary to keep the house cool. This results in poor performance and higher energy bills for you as a result.

A dirty evaporator coil can prevent your unit from functioning correctly and lead to expensive repairs. If your coil is dirty, contact an HVAC professional for help with cleaning.

If your evaporator coil is dirty, it could potentially cause the refrigerant to freeze inside it, damaging both the coil and compressor of your air conditioner.

One way to determine if your evaporator coil is dirty is by comparing the air pressure at both entry vents that take in room temperature air and at output from your AC unit. If these values differ significantly, it may be time for professional cleaning of your coils.

Maintaining your evaporator coil can extend its life and save energy costs. Get in touch with Jerry Kelly Heating & Air Conditioning to discover more about our comprehensive AC maintenance services.

3. Low Refrigerant Levels

If your AC is low on refrigerant, it won’t be able to efficiently transfer heat from inside to outside and may also struggle with effectively eliminating moisture from the air.

Low refrigerant in a window air conditioner may indicate that it requires service by an HVAC specialist. A lower level of refrigerant can lead to various issues with its operation and eventually result in complete breakdown.

Here are some of the warning signs that your air conditioner is low on refrigerant:

No Cold Air:

If your air conditioning unit is low on refrigerant, it won’t be able to cool the air blown over its coils properly. Furthermore, cooling may take longer since it must work harder to reach the temperature set by your thermostat.

Long Cooling Cycles:

Another sign that your air conditioning is low on refrigerant is if it takes longer to cool the home, leading to higher energy bills.

Water Pooling Near The Heater: If your refrigerant levels are low, you may notice ice buildup around your AC’s refrigerant lines and on the furnace. These puddles could be signs that your system needs service from an HVAC specialist.

4. Bad Electronic Board

When a window air conditioner freezes up, it typically indicates an issue with its electronic board. This critical component controls both the fan motor and compressor circuits of the air conditioner.

It is essential to check this board frequently as it can be the source of various issues, including frozen coils. The board is commonly referred to as a logic circuit board or PCB.

If you have a multimeter, you can test the board for continuity by disconnecting its wiring from the unit and using it to measure each connection with its expected voltage. If no power appears, then unfortunately the board needs replacing.

You can inspect the board for scratches, burn marks or misplaced solder. Scratches could indicate a problem that requires professional repair work or replacement of the board.

Another way to diagnose an electronic board is by looking at its schematic. Components like capacitors, diodes and microprocessors may break down over time due to wear-and-tear; this is usually why a circuit board needs repair or replacement.

5. Leaks

There are a variety of reasons your window air conditioner may freeze up, but most can be resolved without needing professional repair or purchasing a new unit.

All air conditioning units work by the same principle: a gas (the refrigerant) cools down as it expands and then contracts. Window ACs use similar physics, but when temperatures drop below freezing the evaporator coil can quickly turn to ice and stop blowing air.

Ice buildup is not an uncommon issue with older window ACs, so it’s essential to diagnose the problem as soon as you observe ice formation. You have two options: do some simple fixes yourself or have a technician inspect and replace your unit if necessary.

Some common causes of this problem include a dirty filter, lack of refrigerant and an inefficient fan motor. If these issues aren’t addressed, the ice will remain frozen and you’ll have to replace your entire unit. To prevent accumulation of ice on your windows, be sure to regularly clean or replace air filters and keep outdoor temperatures reasonable when using window air conditioners.

6. Dirty Window Seal

The window seal is an integral component of any Insulated Glass Unit (IGU) window system. It helps keep heat out in wintertime and keeps your house cool in summertime by trapping air inside your house.

Modern double pane windows are filled with inert gas and then sealed to keep it inside and act as an insulator. Unfortunately, over time these seals fail and the gas escapes, allowing moisture to seep in.

Cheaply manufactured double pane windows often develop this issue, leading to dirt and grime buildup between the panes of glass. If you notice this, it could indicate that your window seal has failed and you should consider replacing its units or installing more energy-efficient options.

Another indication of a failing window seal is if you notice water droplets, fog or frost between the panes of glass. This typically occurs due to temperature differences between indoors and outdoors; condensation then forms between these surfaces.

If you spot this, take action right away as ice can do serious damage to your window and frame. Frost has the potential to discolor paint on windows, rot wood frames, warp glass and even lead to toxic mold and mildew issues.

7. Incorrect Installation

Window air conditioners work to cool a room by circulating refrigerant gas through coils. This cycle of expansion (cooling) to condensation (radiating) occurs continuously throughout the entire run time of the device.

When the coils aren’t adequately cooled, moisture can build up and form on them – this is known as ice formation. This could be caused by a number of things such as a dirty filter, clogged evaporator coil or low refrigerant levels.

Most ice problems can be remedied by identifying and correcting their source. For instance, if an air filter is dirty or clogged, cleaning or replacing it usually solves the issue.

Another potential issue is a malfunctioning compressor. When this occurs, it may not pump enough refrigerant into the coils to cool them to temperatures that shut off the unit automatically. This leaves the coils excessively cold and moisture can form ice on top of them.

If the compressor is malfunctioning, it may be more cost-effective to replace the entire unit. Furthermore, damage to a fan motor could prevent sufficient airflow over evaporator coils and cause freezing issues; inspect both motor and wires regularly for signs of trouble.

Final Tips

In conclusion, if your window air conditioner is freezing up it may be time to do some troubleshooting. Whether it needs a deep clean or you have to check the temperature in the room. These 7 reasons may have the cause for window air conditioners to freeze up. You can always ask a professional to help you assess the condition of your air conditioner. Also you can ask to provide some advice if the problem persists.

If you decide to take matters into your own hands, don’t forget our main tips:

Inspect the air filter and clean the evaporator if needed.

Check temperatures inside and outside your home; check power functions.

Pay attention to humidity levels.

Maintain proper airflow with an open window in front of the unit; look for stale materials near or connected with your unit; inspect for signs of leaking oil from moving parts. Hopefully our tips may help you resolve any challenges caused by freezing up!

Extra Tips

Window air conditioners can freeze up for several reasons, including low refrigerant levels, clogged air filters, or a malfunctioning thermostat. To prevent this from happening, here are some DO’s and DON’Ts:


  1. Clean or replace air filters: Dirty or clogged filters can obstruct the airflow and cause the evaporator coils to freeze. Clean or replace the air filters at least once a month during the cooling season.
  2. Check the refrigerant levels: Low refrigerant levels can cause the evaporator coils to freeze. If you suspect that your AC unit has low refrigerant levels, contact a professional to have it checked and refilled.
  3. Inspect the thermostat: Make sure that the thermostat is set to the correct temperature and that the temperature sensor is functioning correctly. If it’s not, you may need to replace the thermostat.
  4. Keep the room well-ventilated: Ensure that the room where the AC unit is installed is well-ventilated, and the doors and windows are not obstructed.
  5. Regularly maintain your AC unit: Conduct routine maintenance, such as cleaning the coils and fins, checking the drainage system, and lubricating moving parts, to prevent future freezing.


  1. Set the thermostat too low: Setting the thermostat too low can cause the evaporator coils to freeze. Avoid setting the thermostat lower than 68 degrees Fahrenheit.
  2. Block the air vents: Ensure that the air vents are not obstructed by furniture, curtains, or other objects, as it can impede the airflow and cause the evaporator coils to freeze.
  3. Run the AC unit continuously: Running the AC unit continuously without giving it a break can cause the evaporator coils to freeze. Turn off the AC unit for a few hours daily to prevent this from happening.
  4. Ignore signs of malfunctioning: If you notice any signs of malfunctioning, such as strange noises or decreased cooling efficiency, address the problem immediately. Delaying repairs can lead to more severe issues down the line.

By following these DO’s and DON’Ts, you can keep your window air conditioner functioning correctly, without any freezing problems.


Q: Why is my window air conditioner freezing up?

A: There are several reasons why your window air conditioner may be freezing up, including low refrigerant levels, a malfunctioning thermostat, clogged air filters, or obstructed air vents.

Q: How do I prevent my window air conditioner from freezing up?

A: To prevent your window air conditioner from freezing up, make sure to clean or replace air filters regularly, check refrigerant levels, inspect the thermostat, keep the room well-ventilated, and conduct regular maintenance.

Q: Can I continue to use my window air conditioner if it’s freezing up?

A: It’s not recommended to continue using your window air conditioner if it’s freezing up, as it can cause further damage to the unit. Turn it off and address the issue immediately.

Q: How can I thaw my frozen window air conditioner?

A: To thaw a frozen window air conditioner, turn off the unit and allow it to thaw naturally. You can also speed up the process by using a hairdryer on low heat or a fan.

Q: When should I call a professional for help with my freezing window air conditioner?

A: If you have tried the basic troubleshooting steps and your window air conditioner is still freezing up, it’s time to call a professional for help. Additionally, if you notice any signs of malfunctioning, such as strange noises or decreased cooling efficiency, address the problem immediately.

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