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Why Is My AC Freezing Up?

If you’ve ever been told that your air conditioner has frozen over in the middle of summer, you’ve probably found yourself experiencing one prevailing feeling: confusion. If it’s boiling hot and oppressively humid outside, how on earth is it possible that your air conditioner has frozen over? Well, the unfortunate truth is it’s far more likely than you may have ever thought. In fact, this problem inflicts thousands of different homes and businesses each and every year.

To help you better understand this issue and learn how you can avoid it, read on!

What Causes Your Air Conditioner to Freeze?

So what causes an air conditioner to freeze over? Running too much? Setting it too cold? Is it a sign of some other deeper-rooted issue? The answer to all of these questions is… possibly. First, let’s cover the scientific explanation of why your air conditioner freezes.

Have you ever left a glass of ice water on the counter? After a few minutes’ time, you’ve probably noticed that the outsides of that glass are covered in a thin layer of water that’s stuck to the sides. This is called “condensation,” and it’s basically water that has been removed from the air through a process that goes by the same name. Think of it sort of like the opposite of boiling water—when you boil water, it turns from a liquid form into vapor, or gas. When water condenses, it goes from its gas form back into a liquid. It does this by coming into contact with a surface that’s suitably cold enough.

What does that have to do with your air conditioner? Quite a bit, actually. The air in your home has quite a lot of water vapor in it. This is perfectly normal, and in fact not having enough vapor can actually result in things like dry skin or cracked lips. However, when you run your air conditioner, your indoor condenser coil becomes extremely cold due to the frigid refrigerant running through it. As air is forced over this coil to cool it off, the water vapor in the air comes into contact with the coil, causing it to instantly condense back into water.

Under normal circumstances, this water will accumulate and drip off the coil down into your drain pan, where it is carried away via your drain line. However, should something be wrong with your air conditioner, this may not happen as it is supposed to, and the condensation simply can’t escape. When this happens, the condensation process can continue on to the next step—freezing. When this condensation water freezes, it forms ice that slowly builds into a considerable amount, ultimately causing your air conditioner to freeze and stop working.

Here are a few common causes of problems that cause your air conditioner to freeze over:

An Old Air Filter

When your air filter becomes old and full of debris, it can’t allow the same amount of air to pass through. That means that there isn’t enough air to fill the refrigerant in the coil with the heat it needs to continue functioning properly. When the refrigerant remains too cold, it causes the water to freeze far faster, resulting in your air conditioner freezing over more quickly and more frequently.

A Dirty Indoor Coil

Somewhat related to an old or dirty air filter, a dirty indoor coil is one that is more likely to freeze over. Dirt and dust that accumulates on a coil act as a sort of heat shield or blanket that prevents heat transfer from occurring. When the refrigerant in a coil can’t absorb heat, the coil can’t cool your home effectively. When your home doesn’t cool, your thermostat keeps your air conditioner running. When your thermostat keeps your air conditioner running, your air conditioner continues trying to produce cold air, eventually resulting in refrigerant reaching sub-freezing temperatures and causing any water vapor on the coil to freeze over. When it freezes over, it restricts airflow, damages components, and eventually shuts your entire air conditioner down.

A Faulty Blower Fan

A faulty blower fan may result in your air conditioner freezing as well. A faulty fan either doesn’t blow enough air over the coil, or simply blows the air too quickly, resulting in an expedited freezing process. Either way, you’ll find your air conditioner is freezing over far faster if you have a faulty fan, and you’ll need to replace your fan to get your air conditioner working properly again.

What to Do If Your Air Conditioner Freezes

What should you do if your air conditioner freezes over? The first thing is shut your air conditioner off entirely, including your blower fan. Let the system take time to defrost. If you’d like, you can use a gentle heat source like a hair dryer to try and expedite this process if you can get access to the coil itself (if you aren’t comfortable doing this, don’t worry about it, just give it time and the coil will defrost). The second thing you should do is call for help from a professional right away. A professional can help you identify the source of your problem and help you prevent this freezing issue from ever happening again.


Call the experts at HomeWiz at (617) 744-7549 today or contact us online if your air conditioner has frozen over and let us take care of the problem for you!


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