In the middle of August, during a heat wave, while the sun is beating down, the last thing you want is a busted air conditioner. One of the first signs of AC trouble comes in the form of ice. Blocks of ice or even icicles can form around your AC unit and can not only cause leaking and block the outflow of cold air, but also serious damage to your unit, causing it to break completely. Whether your home has window units or central air cooling, a frozen AC unit is a common problem that, luckily, has common solutions. We’ll explain a little bit about how your air conditioner works, what causes it to freeze up, and some important ways you can fix the problem and ensure that your summer lifesaver keeps providing cooled air all season long.

How Does Your Air Conditioner Work

Without going into too much physics, it’s important to know that your air conditioner runs on a simple scientific principle: when gas expands, its pressure — and therefore temperature — decrease. On the other hand, when gas compresses, its pressure and temperature increase. This thermodynamic fact explains how air conditioners work. The refrigerant inside of your air conditioner’s evaporator coil expands, causing the temperature of the coil to decrease. Your unit pulls in your home’s warm air, runs it past the cold coil, and it comes into your house cool. The refrigerant absorbs the heat, or energy, from the air and releases it outside.

Your AC unit is a perfectly balanced physics masterpiece that keeps you comfortable inside your home no matter how hot it is outside. But, when that perfectly balanced physics masterpiece isn’t as balanced as it should be, you get problems: namely, your AC freezing up.

Why Is Your AC Freezing Up?

There are, in general, only a few things that could cause your AC unit to freeze up.

1. Not Enough Air Flow

Our elementary physics lesson above makes it clear that for an AC unit to work properly, there has to be a sufficient amount of air flowing through the unit to exchange the heat from the expanded refrigerant inside the evaporator coil. The condensation that occurs around the coil is usually whisked away by the exchange of heat. But if the unit isn’t receiving enough air, that condensation doesn’t heat up. Instead, it freezes.

2. Not Enough Refrigerant

An integral part of a successful air conditioner is the refrigerant that courses through the evaporator coil. Not only does it expand to create the cold coil, but it carries out the heat from your home’s air and releases it outside. If your unit is running low on Freon, then it is forced to expand more to fill the space. The more it expands, the colder it becomes. Air conditioners are programmed to work best at certain temperatures, so making sure the coil doesn’t get too cold is important. If the refrigerant expands too much and the coil temperature drops too low, the coil freezes and builds up ice that threatens water damage, complete blockage, and a non-functioning AC unit.

3. Mechanical Failures

Sometimes your frozen AC unit is the result of a mechanical failure. The most common part to break is the blower fan, which helps to suck out the warm air from your home and replace it with the new cold air. Because colder air is denser, it doesn’t flow as easily as warm air, so the fan is essential in getting cold air out. If the warm and cold air don’t switch places, a pressure problem within your unit can cause a backup, leading to the formation of ice.

What to Do When Your AC Unit Freezes Up

Now that you know what might be causing the air conditioner problems, it’s time to decide what to do when your AC unit freezes up.

1. Clean Your Air Filters

The most common cause of an air conditioner freezing up is the lack of airflow. The most common solution to this problem is to clean the air filters. You don’t want dust and other airborne irritations to get into your AC unit, so your air filters collect them and keep your unit safe. This means, however, that the filters need to be cleaned regularly to make sure that the dust isn’t blocking your home’s air from getting in.

2. Add Refrigerant

If your air filters are clean, the next thing to do is ensure you’ve got enough refrigerant in your system. Check your owner’s manual or consult an HVAC professional if you’re unsure how much or what kind of refrigerant you should put in your air conditioner.

3. Check for Mechanical Deficiencies

The blower fan can prevent the cold air and warm air from changing places and cause a frozen air conditioner. But there is more that could be broken. After checking for a fully functioning blower fan, check to make sure there isn’t a kink in your refrigerant lines, preventing it from reaching the evaporator coil. If that looks to be in place, take a look at your duct work. There could be a blockage restricting air flow.

Tips and AC Maintenance to Avoid a Frozen AC Unit

It’s always best to prevent a frozen AC unit before it happens, so make sure to take care of your air conditioner so that it can take care of you all summer long. Make sure to never run it when it’s cold outside, as that will throw the pressure out of balance and cause freezing. And make sure to clean your coils regularly. Dust can prevent water from absorbing fast enough, which can cause faster ice build up. Along with cleaning the air filters regularly, make sure to keep the rest of your air conditioner clean for optimal performance.

Air conditioners can seem intimidating, especially when they begin to show signs of failure like freezing up. But with a quick physics lesson and a little bit of care, you’ll know what to do when your AC unit freezes up. If these tips and tricks don’t help, it may be time to replace your unit. Always contact an HVAC professional for major problems and have your units inspected regularly to ensure proper function and efficiency so that you can stay cool even in the hottest weather.

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