How to Fix Your AC Freezing Up (The Ultimate Guide)


It is a hot day outside, and your AC isn't working.

You check your system, and you see it is all frozen.

If you are wondering why and what to do? This article is for you.

Jump to Section

  1. The simple science

  2. Why this happens

  3. Lack of airflow

  4. Refrigerant issues

  5. How to fix a frozen AC?

The Simple Science

Your air conditioning system is a giant refrigerator.

It uses the same concept your kitchen fridge uses to cool your food, except at a much larger scale.

The main components of your air conditioning system are a compressor, a condensing coil, an evaporator coil, a metering device (expansion valve), a blower fan, and of course, the refrigerant.

If any of these components are not working within the manufacturer's specs, it can cause your air conditioning system to freeze.

In a central mini-split system, your evaporator coil freezes; if you have a heat pump, your external coil can also freeze.

The system freezes because the refrigerant levels in the coil are below the freezing temperature of water, 32 degrees Fahrenheit.

The refrigerant doesn't freeze; instead, the moisture in the air condensates on the coils and freezes into a block of ice.

Eventually, the ice can get thick enough that it blocks the airflow.

Why This Happens

There are a few reasons that can cause your AC system to freeze. They are:

  1. Lack of airflow

  2. Refrigerant issues

Lack of airflow

Lack of airflow will cause your system to freeze.

Let's explain.

The evaporator coil absorbs heat from the airflow. This is what cools the air coming into your home.

Suppose there is not enough airflow to your system. Then the coils will stay below freezing temperatures causing the coil to freeze up.

There are many reasons your system may not have enough airflow.

It can be that your ducting is undersized, limiting the airflow to your system.

Also, dirty filters or blocked return vents can restrict the airflow to your ac system.

Both of these will generate high static pressure in your system.

This will cause your system to freeze and will also cause it to work harder than it should, decreasing its lifespan.

A faulty blower fan can also limit the airflow in your ac system.

If you have a variable or two-stage system, your system must communicate electronically with the blower fan, letting it know at what speeds.

A faulty blower will either not receive the proper communication from the system or not operate at the required speeds.

Therefore, a faulty blower fan can lead to a lack of proper airflow in your system, causing your evaporator coil to freeze.

Refrigerant Issues

If you are unfamiliar with how your AC system works, it is a system of components that operate similarly to a refrigerator.

Except it does this at a much larger scale.

Your AC system uses refrigerant to cool your home.

If the refrigerant levels of your AC system are not in line with manufacturers' specifications, it can cause your AC system to freeze.

Low refrigerant levels will mean your system is operating with low pressures—the lower the pressure, the lower the temperature of the refrigerant‍.

When it is low on refrigerant, the temperatures will drop below the freezing point of water.

When the evaporator coil temperature drops below freezing, the condensation on the coil will freeze.

It is important to note that it is not the refrigerant that is freezing but rather the condensation generated on the coils from the humidity in the air.

As your system keeps running, more ice will be built up.

Eventually, this will block all the airflow, not allowing air to get blown through the system.

The ice build-up should be the least of your worries, however. The cause of the ice build-up is more concerning.

The refrigerant won't evaporate completely if the cause is a lack of airflow.

This can lead to liquid refrigerant entering your HVAC systems compressor.

Unfortunately, liquid cannot be compressed, and if fluid enters your compressor, it can cause damage to the point where your compressor needs to be replaced.

High refrigerant levels are also dangerous to your system. Too much refrigerant can also lead to a damaged compressor.

Again, if liquid enters your compressor, it can cause permanent damage to it.

You should contact an HVAC professional if your AC is freezing. You want to be sure your system is functioning correctly to avoid damage.

Another possible problem can be the expansion valve. It is a valve that facilitates refrigerant flow to the evaporator coil.

Its function is to lower the pressure of the refrigerant in a controlled manner.

It reduces pressure, leading to the refrigerant reaching cold temperatures to cool your home.

A faulty expansion valve won't facilitate this pressure drop correctly, which can cause your ac system to freeze.

How to Fix a Frozen AC system

Now that you know what causes an AC system to freeze, you probably wonder how to fix it?

To start, we recommend that you do not operate your AC if your system is freezing.

Doing so can cause damage to your system.

First, you want to remove the ice build-up.

The fastest way to do this is by turning on your heater (don't do this if you have a heat pump).

If you have a gas furnace, the heat will melt the ice.

You also want to ensure that the ac drain line is not clogged.

If it is, you want to be sure to clean your ac drain line before doing so.

Otherwise, as the ice is melting, your furnace will leak water.

After the ice has melted, see if anything limits the airflow to your system.

It can be that your return air vents are blocked, or you may need to replace your air filter.

If it seems as if nothing is restricting the airflow, it can be more serious such as undersized ducting, dirty coils, or a problem in the refrigerant system.

You should contact an HVAC professional if it appears to be a more severe issue.

Undersized ducting requires adding additional ducting.

And adding refrigerant or repairing a refrigerant leak can only be done by an HVAC professional.

Either way, you should NOT run your ac system.

This can cause more damage to your system.

Furthermore, an HVAC pro will not perform any work on a system with a completely frozen coil and would need to return when it is defrosted.

Therefore you should let the ice melt before an HVAC technician arrives to save yourself and the technician's time.

If you have any questions, don't hesitate to get in touch with us. We are here to help.