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What Causes an Air Conditioner to Freeze Up?


On a hot and humid day, you’re unwinding and cooling off when your air conditioner unit suddenly stops working, and then you discover your AC freezing up in the middle of the heat.

Air conditioners can freeze up during the hotter months too, though this is unusual.

In this article, we will look at what causes an air conditioner to freeze up and how to prevent it from happening.

How Does an AC Unit Produce Cold Air?

Knowing the basic concepts of how an air conditioner works will help you understand the functions of its many different parts. Air conditioning works by transferring hot air from your home to the outdoors.

The evaporator coil, compressor, condenser coil, and refrigerant are the four major components of the system. There are three steps in action:

  • Warm air is filtered and blasted over the evaporator coil from the return vent. The extremely cold refrigerant absorbs the heat, which converts from liquid to gas. Then, cool air recirculates throughout the house.
  • The refrigerant is sent outside to the compressor, which is compressed and heated.
  • The third stage is where the condenser transfers the hot air outside. During this step, the coolant returns to liquid and circulates again in this closed-loop system.

What Happens When an AC Starts to Freeze?

Air conditioners are cooling systems, but they’re not supposed to freeze. It is not in their design. If this happens, then the cooling system is not functioning correctly.

Once AC freezing happens, it will not be able to cool the house as effectively as it should. The air conditioner can also act in unexpected ways. This situation should not be allowed to continue.

What Causes an Air Conditioner to Freeze Up With Ice?

You may be a little concerned when your air conditioner gets frozen. Problems with the airflow inside the AC unit or issues with the refrigerant flow can cause your AC unit to freeze. Here are some common causes of your air conditioner freezing up:

Low Refrigerant

If your air conditioner freezes, your outdoor unit may be low on refrigerant. This material is a cooling liquid that cools the air entering your home. However, your AC system needs enough of it for this substance to work effectively. This refrigerant is used by the outdoor AC unit, known as the compressor, to pump cooled air inside your home.

When there isn’t enough refrigerant in an AC system, the pressure inside the unit drops and causes temperatures to fall below freezing in the evaporator coils. When this happens, nearby water vapor could stick to these coils and cause them to freeze.

However, you can’t add more refrigerant since professionals don’t recommend this option. An AC unit has a closed system, a refrigerant doesn’t evaporate, and low refrigerant levels frequently signal a leak. If you have an air conditioner freezing up, contact a certified HVAC technician to inspect for leaks.

Weak Air Flow

In an air conditioning system, airflow is essential. If the air isn’t flowing correctly, the HVAC system isn’t going to perform adequately. Poor airflow could be the cause of frozen air conditioners.

Faulty Blower Fan

The blower motor and fan help to blow warm air over the coils in the system, which helps to create cooler air. Cool air will not come out of your vents when the blower fan quits working. This can result in a frozen AC. Check the blower motor and fan when you’re unsure what to do when your AC unit freezes. If this is the problem, you will hear rattling sounds from your air conditioner.

Insufficient Power to the Fan

In other cases, the issue may be with your home’s electrical system. Since an air conditioning unit consumes a lot of energy, a few system components may fall behind. For instance, your fan or blower motor may not get enough power output. If this is the case, the air conditioner may freeze.

Air Duct Problems

Your AC air ducts are critical to the operation of your system. However, difficulties might arise at any time. These air duct issues can result in severely insufficient airflow, which ranges from leaks to clogs.

If you have an issue, such as damaged air ducts, the warm air inside your home may struggle to travel over the evaporator coils, resulting in condensation. Schedule a duct inspection appointment with an expert when your air conditioners freeze up for them to check whether there’s weak airflow coming from your vents.

Blocked Air Filter

A blocked and dirty air filter is another common cause of your AC freezing. You should clean and maintain your AC filters since they have a significant impact on airflow. The flow of warm indoor air is restricted when the filter gets blocked with particles.

Clogs on an Evaporator Coil

Not only should you avoid ice in your cooling system, but you should also avoid dust in it. Dust can readily develop on your AC evaporator coils caused by dirty air filters. Dust can easily adhere to these coils because they are frequently damp from the surrounding wetness.

Since dust acts as an insulator, it is difficult for cold air to escape an evaporator coil, which can cause ice buildup in your AC unit. Thick sheets of ice can form as excess moisture continues to collect.

Frozen AC Unit Due to Cool Summer Nights

Air conditioners are tuned to function within a set of ideal temperature limits. It usually happens in other countries, but an AC can malfunction when summer nights have colder outdoor air than the optimal point can tolerate.

Tips for Troubleshooting a Freezing AC Unit

It is frustrating to be in that situation when your air conditioner freezes. Now that you know what is causing your AC unit to freeze, here are some basic troubleshooting procedures you can do for an AC unit freezing up:

Air Filter

The first step is to check that the air filter allows the system to operate correctly. It is a quick remedy for a frozen air conditioner. If you have dirty filters, this will block proper airflow, which generates ice formation and results in poor performance and inefficient operation. For best performance, you should replace the air filters every three months.

Refrigerant Leak

To resolve an AC freezing issue, look for refrigerant leaks. Detecting and repairing leaks will require the expertise and instruments of an HVAC technician. If you suspect refrigerant leaks, call a professional immediately.

Blower Fan

Look for broken or damaged blower fan components, as well as strange noises when the machine is running. Problems in the components can cause an AC unit to freeze or function poorly. An HVAC professional is required for detailed checks, which include inspecting the motor’s condition, the fan’s rotation speed, and the power.

Air Vents

A properly running system requires unrestricted air circulation in the supply and return vents. Furniture, other barriers, and closing too many vents might cause the AC unit to freeze due to too much restriction.

Drain Line

When the air conditioner eliminates humidity, it must go somewhere. Examine the drain line and drip tray for any signs of clogging that could cause frozen evaporator coils. Some issues may be simple to resolve, while others would require the services of an HVAC professional.

How Do I Keep My Air Conditioner From Freezing Up?

There are ways to avoid an AC freezing up. Once you’ve prepared these preventive measures, you should be able to avoid this situation.

Change Your Air Filters Regularly

The simplest way to avoid having an AC unit frozen is to change your air filters regularly. Changing them depends on the size and type of filter you own, the number of people living in the same residence, and whether or not pets are present.

Schedule Regular Maintenance

Create a preventative maintenance plan. Have an HVAC professional inspect your system before the warm weather comes in full force. Air conditioning service will help you avoid a frozen air conditioning unit and other AC repair issues while extending your HVAC system’s life.

Plan an AC System Tune-up

Request that your technician inspect your air filters for filth, your AC coils for grime, your refrigerant level for leaks, your drain for blockages, and your blower fan for appropriate rotation and speed.

Evaluate Your Air Ducts

An HVAC expert can evaluate your air ducts for appropriate ventilation, which is crucial. It might be difficult sometimes due to the complexity and difficulty of accessing your air ductwork system. But it’s essential to have this checked to help you avoid massive and more expensive issues in the future.

Final Thoughts

As we know, air conditioners freezing up is a common and frustrating problem for homeowners. Regardless, you can avoid this with suitable supervision.

Don’t hesitate to contact a professional HVAC service for regular maintenance and check-up. They will keep your air conditioning system in excellent condition for years if done often.

JP Reyes

JP has been in the aircon industry for almost as long as he has been alive. As a child JP would help his tatay fix aircon units at their junk shop in Cavite. After graduating UP in the early 2000's, JP then started his own Aircon servicing business and within 5 years had 10 shops in 8 different cities. Fast forward to today and JP brings all his experience and expertise online to give readers trustworthy advice and reviews about Air-conditioning buying, servicing, cleaning and repair in the Philippines.

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