frozen snow covered AC unit outside

Isn’t it perplexing how an air conditioner can freeze up in the middle of summer? Many homeowners experience this issue, yet they are not knowledgeable about what causes air conditioner to freeze up and how to fix it.

So, what causes air conditioner to freeze up? This article will discuss the most common causes of your air conditioner freezing and what to do about it.  But first, let’s learn a bit more about your air conditioner and how it works.

Also, if you are looking for space heating methods for your home as you approach wintertime, you may be interested in the best oil filled space heaters for your home.

How Does an Air Conditioner Work?

An air conditioner uses a refrigerant to facilitate the cooling process. The refrigerant is a chemical that vaporizes when pushed into the evaporator coil.

When you turn on the air conditioner, the blower fan starts to run, and then almost immediately, the compressor comes on. The blower fan pulls hot air from the room into the air conditioner while the compressor compresses the vaporized refrigerant causing it to expand in the evaporator coil.

The Joule-Thomson Effect in thermodynamics demonstrates that when gas is pressurized, it expands, causing it to cool down or heat up depending on its chemical properties.

In this case, the refrigerant expands inside the evaporator coil and cools down. Since its temperature is significantly lower than the incoming warm air, the temperature gradient causes heat transfer from the hot or warm incoming air to the refrigerant via the evaporating coils.

A malfunction in the AC unit disrupts this process, causing the refrigerant coil to cool excessively, resulting in a frozen air conditioner.

Top 5 Air Conditioner Malfunctions that Could Cause it to Freeze

1. Restricted Airflow

An air conditioning unit depends on the continuous flow of hot air into the unit and out of the unit to operate efficiently. If the airflow is restricted, it can cause the refrigerant to cool down to a freezing point. There are different causes of restricted airflow in an air conditioner, including:

Faulty Blower

The blower fan of the AC unit is responsible for pulling in hot air and pushing out cool air back into the room. If it breaks down, this process becomes disrupted. A blower motor can break down due to discharged capacitor, or the blower itself gets broken.

Loss of Power to the Fan

The fan has a similar operating mechanism as a blower. The main difference between them is that the fan pulls atmospheric air to cool the vaporized refrigerant and pushes out the hot air.

If the fan is not operating efficiently, it curtails the proper airflow equilibrium in the air conditioner. A low voltage power source can cause a loss of power to the fan. Or, it could be incidental, particularly after a blackout.

Clogged or Dirty Air Filter

Air filters trap dirt and dust from the intake air. Over time, they collect too much dirt, causing the pores to become blocked. As the result of a dirty filter, airflow to the unit becomes restricted. Even if your blower fan is in tip-top condition, it will not be able to pull in sufficient amounts of air because of the dirty or clogged air filter.

Blocked Vents

If you place your air conditioner too close to furniture or a wall, it may block the vents, hindering proper airflow in and out of the unit.

2. Dirty Evaporator Coil

Although the air filter does a great job keeping dirt and dust out of the air conditioner’s interior, some dirt and dust may still manage to sneak it to the air conditioner unit. It layers up on the surface of the evaporator coils and acts as an insulator. This inhibits the heat transfer between the refrigerant and the intake air.

3. Excess Moisture Within the Air Conditioner

During the operation of an air conditioner, water accumulates on the various components due to condensation. Also, moisture is removed from the intake of humid air. The water collects and is drained out either automatically or manually. If the draining system is blocked or the unit is not drained in time, the moisture can deposit on the evaporator coils, causing the refrigerant to cool down.

4. Low Refrigerant

Every air conditioner is designed to operate on a given volume of refrigerant. Due to the constant vaporization and condensation of the refrigerant, it may lose volume over time. Or, there might be a leak within the refrigerant lines.

Therefore, when compressed, there is a significant drop in pressure in the evaporator coils, which can cause the refrigerant temperatures to dip to a freezing point. Consequently, the temperature of the surrounding water vapor or moisture in the air conditioner drops. It may also freeze, causing frost or ice on the surface of various internal components.

How Can You Tell if the Air Conditioner is Freezing Up?

First, check the registers. If they are warm, the evaporator coils are frozen. You could also open the unit and inspect the internal components for ice. However, note that the refrigerant may be frozen, yet there may not be any ice.

How Can You Prevent Your Air Conditioner from Freezing?

There are several measures you can take to prevent your air conditioner from freezing. They include:

  1. Regularly cleaning the air conditioner. This maintenance procedure is critical for preventing your air conditioner from freezing. It prevents excessive dirt and dust accumulation on the air filter, condenser coils, and evaporator coils. You should clean your air conditioner at least once every month. Ensure to replace the air filter within the timeline stipulated by the manufacturer.
  2. Regularly inspect the air conditioner and HVAC system. Whenever you have a chance to take apart the air conditioner, inspect each of its components carefully for leaks, corrosion, or signs of tear and wear. Regular inspections of your HVAC system allow you to catch problems early on before they proceed to cause a major power breakdown.
  3. Plug the air conditioner into the correct power source. Low voltage may cause a loss of power in the blower fan and compressor. It could also overdraw the power outlet or lead to short-circuiting.
  4. Servicing the air conditioner. An air conditioner should be serviced every 1-2 years, depending on the frequency of use and the climatic conditions. If you use it for most of the year or live in climatic conditions where it is extremely hot and humid, you should service It every year. The main goal of servicing is inspecting the components to ensure they are in good condition. It is also an opportunity to check the refrigerant levels and refill it if necessary.
  5. Drain the air conditioner regularly. If you drain your air conditioner manually, you need to do it every 1-3 days to prevent excessive water accumulation. The more convenient option would be to automate the draining process. You could either install a drain hose or a condensate pump.

Regularly check the drain line to ensure that it is not blocked. As part of your cleaning routine, ensure to clean the drain line too.


If you suspect that your AC is frozen, you can attempt to troubleshoot the cause by yourself.  First, check whether it is releasing cool air. If not, inspect the air conditioning unit for ice or a refrigerant leak.

Check the drain line to ensure it is not blocked, and there is no ice. If you haven’t cleaned the unit recently, give it a thorough wash and change the air filter if needed. If the problem persists, contact an HVAC specialist to inspect the unit, diagnose the issue correctly, and resolve it.