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Question:

Today’s Ask Any Hour Services, Electrical, Plumbing, Heating & Air addresses a common AC problem that happens to many homeowners during the summer. Our techs get this question all the time so we’re going to discuss it here: what do I do if my AC freezes over?

Answer:

First of all, if your AC condenser unit is frozen, stop reading and turn off the AC immediately! A frozen condenser puts a huge strain on your unit and its components and must be turned off right away. The ice must also be melted off before turning it back on to avoid additional damage. Once the AC is off, turn the HVAC fan on, which will force the system to blow warm air over any frozen coils, speeding up the defrosting process. But do make sure it’s set to ON and not to AUTO. Automatic settings cause the fan to start and stop over and over again; you want continuous, non-stop airflow over the frozen areas.

Now that your unit is off, your fan is on, and the ice is melting, let’s take a few steps back. Defrosting your unit can take anywhere from an hour to over a day depending on the amount of ice built up, so let’s settle in and talk about what went wrong and how you should move forward.

You were likely in your house, going about a normal day when you noticed that it wasn’t as cool as it should have been. Perhaps you even put your hand over one of the vents and felt warm air coming out. At this point, you probably started troubleshooting by doing a brief visual overview of your system. This is probably when you noticed the ice covering your condenser unit. But how did this happen?

Even though it’s an issue that seemed to come on suddenly for you, it’s usually evidence of a problem that has been lurking for a while. There are a few main issues that can cause freezing, some of which you may be able to identify yourself. However, it would be a good idea to have a technician come and troubleshoot your system to specifically and definitively pinpoint the problem. But keep in mind that in every case, the issue is usually related to airflow. If the airflow is restricted or interrupted, freezing can occur. Here are some potential culprits:

  1. Dirty Air Filter

    Air conditioners need constant airflow so that humidity can’t settle on the coils and freeze. To keep the air moving freely, you need to be sure your air filters aren’t dirty or clogged. And the best news is that this is an easy fix you can do yourself. Just be sure to set a reminder on your phone to check your filter once a month and change them out as necessary to avoid running into this problem again. The United States Department of Energy reports that changing your HVAC filter can improve the efficiency of your HVAC equipment by 5-15%. Plus, changing your filter regularly is relatively inexpensive; otherwise, air restriction puts strain on your system, which could cause some pretty costly problems. If you suspect a dirty, clogged filter may have caused your problem, it might not be a bad idea to have a technician come and check your system out anyway. The freeze-up may have caused strain to other components that might not be immediately apparent. A system assessment and tune-up could determine if you have any other lurking issues.

  2. Dirty Evaporator Coils

    Similar to the dirty filter, this could be a solution you can address and fix yourself. Greasy, grimy evaporator coils, like dirty filters, can cause air restriction that puts strain on your system and can cause ice to form. We’ve created a video here that you can watch to show you how to clean your evaporator coils yourself. But again, even after you’ve cleaned your coils, you may still want to have a technician come to check your system out to be sure no other components were harmed.

  3. Mechanical Issues

    While they may seem like relatively simple machines, furnaces and condenser units are full of moving parts that can wear down and break. Lines can leak, kink, or clog; fans can seize up and stop working. Any of these interruptions can cause the system pressure to drop, resulting in overexpansion of the refrigerant, which makes the unit too cold, leading to ice buildup. In the case of a mechanical issue, the best thing to do is have an HVAC technician come and inspect your system to see where the problems are and give you options for repairing or replacing those parts.

  4. Low Refrigerant

    Refrigerant is an essential element in ensuring regulated temperature throughout your system. Even though it’s responsible for keeping things cold, a frozen unit can be caused by low refrigerant. Low refrigerant can cause a pressure drop, allowing moisture in the air to freeze around your HVAC coils. Despite what many homeowners may think, refrigerant doesn’t simply get “used up.” It doesn’t decrease over time, and it doesn’t evaporate during AC use. So if you’re low on refrigerant, there’s no doubt you leak.
    In the case of a refrigerant leak, the best idea is to call a licensed HVAC technician. Refrigerant is a hazardous chemical that should only be handled by a professional. Though refrigerants are safe to use in the home, they’re best handled by a professional who knows how to keep them contained.

If you suspect mechanical failure or leaks might be the cause of a malfunctioning AC, contact an HVAC professional to come and diagnose the problem. Even in the case of small problems, you can help prevent bigger issues with your AC by getting regular tune-ups and getting your whole system checked out.

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