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Why Your AC is Freezing Up & What to Do | Petro Home Services

Central AC units

AC freezing up? How can something that works all day during the hottest days of the year be prone to freezing? Despite the ironic happening of an AC freeze in the summertime, air conditioners freezing up is something that happens a lot. Not many homeowners are equipped with the knowledge and understanding about air conditioners to prevent this problem on their own. It’s a problem that can turn a beautiful summer day into a blistering hot one in minutes.

How can you tell if you might be facing a freezing problem?

A sure sign is to check the supply registers. Is it warm? If so, that’s a good indicator of frozen evaporator coils. Open the panel and check for ice. Keep in mind, a lack of ice doesn’t necessarily mean that you’re not having a freezing problem. However, seeing ice is pretty-well a guarantee that your AC is frozen.

Understanding the Joule-Thomson effect:

Before we delve into the causes of an AC freezing up, let’s talk a little bit about how your AC works. First, we must understand that temperature is how much energy a molecule has. When the air feels hot, it’s because the molecules in the air have a lot of energy and are moving around rapidly. The same works in reverse, cold air is comprised of low energy molecules. So, what the Joule-Thomson Effect demonstrates in thermodynamics is when the air in our ACs isn’t compressed, its temperature will decrease as it expands and the molecules slow. When it is compressed, the molecules get excited and heat up.

The point of an air conditioner is to expand the refrigerant inside the evaporator coil so that it cools down, so when it leaves the air conditioner, it cools the air inside your home and effectively removes the hot air from inside the house. However, if something in the air conditioner malfunctions, the whole system gets disrupted. This causes the evaporator coil to allow the refrigerant to cool too much, causing it to fall below freezing and ice over.

So, how can you prevent something in the cooling equation from going terribly wrong? There are three main causes that lead to an AC freeze up. By understanding these causes, you can get out in front of them so you never have to experience an AC freeze. Plus, we’ve included how to fix each cause, so if you do have an unfortunate AC problem, you’ll be able to fix it in no time flat. Keeping your air conditioner in great shape will help it run more efficiently, saving you money on your energy bill, and keep it from becoming an eye sore.

Blocked air flow causes freezing up:

Air conditioners need to have a constant flow of air so that humidity can’t settle on the coils and freeze. In order to keep the air flow in your own house moving enough to not disrupt your air conditioner’s functionality, you need to be sure your air filters aren’t dirty and becoming clogged. This restricts the air flow in your house. Air filters are cheap, and it’s best to change them regularly. Keeping your AC clean and tuned up is also a good idea for preventing air flow problems, and other problems in general. Plus, the United States Department of Energy reports that changing your HVAC filter can improve the efficiency of your HVAC equipment by 5% to 15%.

How to fix it:

Your AC is already blocked, and you discovered that your air filters were clogged. It’s likely a blocked air flow problem. The first thing you need to do is turn off the air conditioner and let it defrost. After it’s had sufficient time to thaw (1-3 hours), turn on just the fan for about an hour. Use this time to change your air filter. You can check out our article on how and when to change your AC filters. After that, your AC should be back to normal working order. 

Mechanical problems or refrigerant leaks?

Air conditioners are full of moving parts that can get stuck, broken, or clogged. Refrigerant lines can kink, fans can stop moving, filters can become clogged, and things can leak. Any of these things causes a drop in pressure, allowing the refrigerant to expand too much and become too cold. Refrigerant is also an essential part in ensuring a regulated temperature throughout your machine. A too-low level of refrigerant is also known to cause freezing up. Some of these problems are easier and cheaper to fix than others. In the case of a coolant leak, any fix is likely to just be a temporary fix. It may be time to consider investing in a new machine.

How to fix it:

Mechanical problems and leak repairs go a bit beyond a short guide to AC freezing. It’s best to tackle these problems with the help of a trained professional who knows how to handle refrigerants. Though refrigerants are safe to use in the home, they’re best handled by a professional who knows how to keep it contained. If you suspect mechanical failure or leaks might be the cause of a malfunctioning AC, contact an HVAC company and have a professional come give the problem a look. You can help prevent catastrophic issues with your AC by getting regular tune-ups by an HVAC professional.

Cool summer nights can cause your AC to freeze:

Air conditioners are calibrated to operate within a certain set of optimum temperature thresholds. When nights in the summer time are colder than the optimum threshold can account for, it can throw an AC out of whack.

Here is some more information on how to change your AC’s air filter.

How to fix it:

Having a programmable thermostat can automatically get ahead of the problem by shutting down the AC when temperatures get below 60 degrees. If you don’t have a programmable thermometer, keep an eye out on the current temperatures each night and anticipate if it’s going to be colder than 60 degrees. In which case, you should turn off your AC and open your windows to let in the cool summer breeze instead.

Summing it up:

A freezing AC is a very common, frustrating problem that homeowners face. However, the problems causing a frozen AC are preventable with some regular maintenance and tune-ups. Tune-ups and changing air filters regularly go a long way to preventing mechanical failures, clogs, and leakages. Hiring a professional HVAC service, such as Petro Home Services, getting an annual AC Tune-up and taking advantage of Maintenance Service Plans, help you keep your AC in tip-top shape, will save you money on your energy bill and help keep your AC unit running for years and years.

Petro Home Services is proud to not only serve communities in DC, CT, MA, MD, NJ, NY, PA, and RI but we also proudly acknowledge the skills and experience of our expert team behind all resources. With insights on topics ranging from heating oil facts to common air conditioning questions, you can rely on Petro Home Services for facts and information to help you understand more about your heating, cooling and home comfort needs. This article and all articles on the Petro Home Services website have been approved by our team of home service experts.