What Causes An Air Conditioner To Freeze Up? (8 Common Causes)

What Causes An Air Conditioner To Freeze Up? (8 Common Causes)

Modern electrical and electronic devices make our lives much easier, but unfortunately, they are not perfect, so sooner or later, the time comes when we have to deal with some of their shortcomings.

One of the devices that brings us much comfort, especially on hot summer days, but which is still not perfect, is the air conditioner.

The thing that can make it imperfect is the formation of ice, which can occur on both indoor and outdoor units. It is somewhat unusual because many people would never expect something like this to happen, which is why they ask what causes an air conditioner to freeze up.

AC not blowing air or turning on is understandable, but actual ice? It depends on what caused this issue, of course. And many things can give rise to it, so read on to learn about them!

What Causes An Air Conditioner To Freeze Up?

1. Blocked Vents

We’ll start with the cause that is not so common but easy to fix because we do not want to immediately create panic by telling you all about big problems which will require you to call a technician to fix your air conditioner.

Yes, we are talking about blocked vents! The reason why this problem is easy to get rid of is that, in most cases, the homeowner is the main culprit that caused it.

Whether it is a piece of furniture, a curtain, or a bigger item you just forgot about, it’s quite simple to accidentally cover the supply or return vents and cause poor or non-existent airflow in the AC system, which leads to the formation of ice in it.

Even if you have not blocked the air vents with some object, it is possible to close too many vents, which will again lead to the problem described in the previous paragraph.

In any case, just check whether you have accidentally blocked or deliberately closed the return and supply vents, and you will find out if you are to blame for your AC’s freeze-up.

2. Low Refrigerant Levels

Freon (cooling agent) is an essential part of your air conditioner unit because it is where all the “cold” comes from, i.e., it is responsible for cooling the air, which, of course, cools your home.

However, long-term use of an AC will eventually lead to some wear and tear of the components in which the freon is located, such as the evaporator coil, refrigerant lines, or compressor, which can result in a refrigerant leak.

When this happens, there will be a pressure drop, leading to a drop in temperature and, of course, ice buildup on the inside AC unit. The air conditioner will also start consuming more electrical energy and start working slower because it will have a hard time keeping the home cold with smaller amounts of freon than usual.

Another possibility that will lead to low refrigerant levels is the HVAC professional not filling the air conditioner with enough freon during the installation of AC. Of course, the chances that something like this will happen are low, but you should keep it in mind and pay attention to it during the repair of the AC system.

3. Dirty Air Filter

Dirty Air Filter
Image Credit: servisliu

An unmaintained, dirty filter is one of the most common reasons for a frozen AC unit.

Over time dust accumulates in the filters creating a thick layer. When this happens, your air conditioner will start “to choke” because it is not getting enough air and can not function properly.

The problem is that the dust acts as an insulator, keeping the cold inside the component and, combined with the moisture that accumulates on the dust, creates an icicle effect.

Similar to the case with a low freon level, this causes less efficient system operation and higher electricity bills, so it is crucial that you eliminate this issue as soon as possible.

4. Dirty Evaporator Coils

Dirt and dust negatively affect not only the air filter but also the evaporator coil. Most often, the dirt on the coils results from a dirty filter, but even without that, it can easily accumulate and stay on them since they are damp from the moisture that is created inside the AC system.

Add to that the already mentioned fact that dust serves as an insulator, and it will be apparent how the cold from the evaporator coils fails to escape and why ice begins to form on them.

5. High Humidity And Low Temperatures

When the requirements for heating are high, and there is high humidity and low temperatures in the outside air, ice can form on the exchanger of the outdoor unit.

In cases like this, ice first appears on the air conditioning compressor and then spreads along the copper tubes. The more moisture there is in the air, the greater the ice cover.

Higher-quality air conditioners have better compressors, which usually achieve normal functioning without allowing ice to form on the outdoor unit.

If ice does appear, such an air conditioner will slightly reduce the power of the air conditioner’s compressor and balance the ice formation and the space-heating effect. The homeowner will not even feel this phenomenon, and the air conditioner will heat their home continuously and efficiently.

However, cheaper air conditioners will take 5 to 10 minutes breaks, during which time they do not heat but melt the ice that has accumulated on the outdoor unit.

6. Faulty Blower Fan Or Blower Motor

Faulty Blower Fan Or Blower Motor
Image Credit: andhika_teknik.ac

Next on the list of things that cause an air conditioner to freeze up is a malfunctioning or not-functioning-at-all blower fan or motor.

These two components work together and are responsible for pushing the hot or cool air out of the AC unit and into the house. The motor powers the fan, while the fan is the part that actually blows out the air.

However, in the event that one of these two things (or maybe even both) does not work properly or at all, the air will remain trapped in the AC. This, of course, means there will be a lack of airflow, which results in the air conditioning system freezing up.

7. Blower Motor Not Getting Enough Power

Even if everything is fine with the blower motor, a situation can occur in which it can not drive the fan because it is not getting enough power. Of course, we learned from the previous problem that a fan that does not work correctly prevents good airflow, which means ice in the air conditioner.

It does not mean that there is something wrong with the blower motor.

Usually, there is a malfunction in the electrical system of your home or the system is simply overloaded and can not power the blower motor at that moment, which is not a rare occurrence in modern households that can have dozens of devices that consume electricity at the same time.

8. Clogged Or Damaged Air Ducts

Air ducts are a very important part of any AC unit since the air that cools or heats the house flows through them. To be more precise, air ducts are used to conduct supply air, that is, outside air that will be used inside the home, or blowout return air, that is, inside air that will be released outside.

Since both of these processes go on constantly, it is not uncommon for dirt to build up and contaminate or block air ducts, which will prevent proper air circulation.

In addition to this, physical damage may occur in the ducts, either due to wear and tear or an outside effect such as a human mistake causing leaks and, again, of course, poor circulation of the air. And as you already know, inadequate air circulation often results in the air conditioner freezing.

It Is Better To Be Safe Than Sorry

It Is Better To Be Safe Than Sorry
Image Credit: kaniongroup

As in the vast majority of situations in life, prevention is the best medicine, which is why you should do everything in your power to avoid AC freeze in the first place. The best way to do this is to schedule a regular AC check-up with an authorized servicer or professional HVAC technician.

Ideally, your air conditioner should be inspected and serviced twice a year, but as long as you do this once a year, you should prevent or at least catch any issue while it is in its initial stages.


Now you know the reasons that can lead to the appearance of ice on your air conditioner.

The number one culprit is low refrigerant (freon) level, which usually occurs due to leaks.

The second biggest cause of this is inadequate or non-existent airflow, which can come about due to many reasons, such as dirty air filters or evaporator coils, blocked vents, faulty blower fans or motors, or congested or damaged air ducts.

Lastly, high humidity and low temperatures can, from time to time, be the reason why ice forms on the AC unit.

Whatever the case, do not forget to call the professionals immediately and have them look at the problem when something like this happens.

And also, do not forget to comment if you have something to ask regarding this topic!

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