AC Unit Frozen? | Common Reasons and Troubleshooting Tips

What Causes an Air Conditioner to Freeze Up?

When the outdoor temperatures are soaring, you depend on your air conditioner to perform. However, just like all machines out there, system issues can happen at some point. While an AC unit can experience several different complications, an air conditioner freezing up is one of the most common. If you have an AC unit frozen up, you’re certainly not alone.

*Do you have an AC pipe freezing? Check out our recent post to learn more about the topic: (link to post)

Keep reading to learn some common reasons why your air conditioner is freezing up, including how to fix the problem and return the cool comfort to your home.

AC freezing up? Check out these common reasons

If you have an air conditioner that’s frozen, you may be a little worried. Luckily, there might be a fast and cost-effective solution. Here are some common reasons why your air conditioning unit is freezing up:

Low refrigerant

If you notice your AC freezing up, your system could be low on refrigerant. This substance is a cooling liquid that cools the air before it enters your home. But for this substance to work effectively, your system needs enough of it. The outdoor unit, called the compressor, uses this refrigerant to pump cool air into your home.

When there isn’t an adequate amount of refrigerant in an AC system, the pressure will drop inside the unit. This will then cause temperatures to fall in the evaporator coils—which can dip below freezing. When this happens, nearby water vapor can grab onto these coils and freeze. This is one of the leading culprits of an AC freezing up. After the initial coat of frost accumulates on the coils, it can eventually build up to a thick sheet of ice.



Think you can simply add more refrigerant? As this sounds like the obvious choice, it isn’t advised by professionals. In fact, since an AC unit is a closed system and refrigerant doesn’t evaporate, low refrigerant levels often indicate there’s a leak. This leak could be found in the refrigerant lines, compressor, or evaporator coil. That said, if you’re experiencing an air conditioner freezing up, call a professional HVAC technician to properly check for leaks.

Poor airflow

Airflow is essential in an air conditioning system. If air isn’t flowing properly, the system probably won’t work very effectively. When there’s an AC unit frozen, poor airflow could be the culprit. However, there are a number of airflow problems that can occur.



Check out the most common airflow complications you could be experiencing:

Faulty blower motor

The blower motor and fan help to blow air over the coils in the system, which helps to create cool air. When this fan stops working, cool air won’t be coming from your vents. This can cause a frozen AC unit. If you’re not sure what to do when your AC unit freezes up, inspect the blower motor and fan. If this is the problem, you may hear rattling sounds coming from your air conditioner.

Not enough power to the fan

On some occasions, the problem could lie with your home’s electrical system. As air conditioners use tons of energy, sometimes a few system components can get left behind. For instance, your fan or blower motor might not be receiving the power it needs. If that’s the case, an AC unit freezing up could be the result. 

Air duct issues

Your AC air ducts are vital for a properly working system. However, they can experience problems at any time. From leaks to blockages, these air duct problems can result in very poor airflow. If you notice your AC freezing up, including weak airflow coming from your vents, schedule a duct inspection appointment with a professional.

Dirty air filter

A dirty or clogged air filter is another common reason why you have your AC freezing up. Since air filters have a significant impact on airflow, you always want to make sure they’re clean. Even if you have a properly functioning air conditioning system, weak airflow through your filters could lead to a very uncomfortable home.

Blockages on coils

While ice is something you never want to see in your system, dust is another one to add to the list. Typically caused by dirty air filters, dust can easily accumulate on your AC refrigerant coils. As these coils are usually wet from the surrounding moisture, dust can stick to them with ease. Since dust acts as an insulator, it’s hard for the cold to escape the coils, potentially leading to ice formation. As moisture continues to accumulate, thick sheets of ice can form.

AC unit frozen? Try these troubleshooting tips

If you have your AC freezing up, it can be a frustrating problem. Luckily, some simple troubleshooting tips can help, which include:

Examine air filter

Since airflow is a leading reason for an air conditioner freezing up, making sure to change your air filters regularly is highly encouraged. Try writing a reminder on your calendar or posting a note on your fridge. Unfortunately, forgetting this simple task is very easy. But given how an air filter is so important for your home, it’s something you definitely want to remember.



Periodically changing your air filters doesn’t only prevent ice from building up, but it also helps to improve your home’s energy efficiency. Furthermore, it can also enhance the performance of your system. Experts say you should change your air filter every three months, possibly sooner if you have pets or allergies.

Check for refrigerant leaks

To get rid of an AC unit frozen problem, you’ll want to check for refrigerant leaks. However, unless you’re an HVAC professional, this isn’t something you should do yourself. Since HVAC techs have years of experience dealing with refrigerant issues, it’s best to leave it to the professionals. If you try a DIY project, you can risk wasting tons of costly refrigerant, or you can make the problem much worse. Calling an expert can save you time, energy, and tons of hassle.



Remember, as an AC unit is a closed system, you never want to simply add more refrigerant. If an HVAC technician wants to add some to your unit, don’t let them and call another provider. Adding more refrigerant only makes the problem worse.

Look at the blower fan

If your system’s blower fan is damaged or broken, this could be causing ice formation. That said, you should also hire a professional to take a look at this system component. Not only can a faulty blower fan lead to an AC freezing up, but it can also significantly decrease system performance. While this can cause many headaches, it can also result in high energy bills.

Inspecting the blower fan is another job that should be handled by a professional. Unless you’re very familiar with how they work, knowing what to look for can be challenging. The technician should check the motor for age and overall condition, but they might also look at the fan’s rotational speed and power source.

Inspect the vents

Another action you can take involves looking at your air vents. Make sure both your supply and return vents are open and free of any blockages. Also, make sure furniture and other belongings aren’t in the way of your vents. It’s also smart to never close more than 2-3 supply vents. Restricting too much airflow can cause your AC unit to freeze up.

Check the condensate drain line

Air conditioning systems work by taking humidity out of the air. When that humidity is taken out, the moisture travels to the condensate drip tray. If your system ever gets clogged, this water can eventually overflow. This can lead to increased moisture in the system, which could cause the evaporator coil to freeze up. To prevent this issue, remove any blockages in the drain line or call a professional for help.

By following the tips in this post, you can restore the cool air to your home while also improving the performance of your AC system.