How to Fix a frozen air conditioner? [Tips for AC Repair and Maintenance]

How to Fix a frozen air conditioner?

Air Conditioner / October 4, 2022

air conditioner freezing up diagram of how it works We are often asked the question, why is my air conditioner freezing up? Figuring out what is causing your air conditioner to ice up can be frustrating, but it is not an uncommon problem. If you’ve read any of our articles, then you know that we are a small, U.S. Veteran-Owned company in Southern California, and pride ourselves on giving honest, straight answers. In fact, most of our posts address either one of two things: first, common air conditioning problems that people have, or second, the questions we get asked most frequently. There are a number of reasons for an air conditioner to freeze up, and it really doesn’t matter whether it is a window AC unit or a central air conditioner – the causes of, and solutions to, an air conditioner that keeps freezing up are exactly the same. It is important to address this issue – a frozen air conditioner will not only cool improperly, but can actually be severely damaged if it keeps freezing up. If you have this problem, you have to address it immediately – it won’t solve itself. In this article, we will tell you what causes a central air conditioner freeze up, and what you can do to fix it.

Standby for a small high school physics lesson. We don’t need to go too in depth, so bear with me, but understanding this principle is the key to figuring out why your air conditioner is freezing up. The Joule-Thomson Effect is a principle in thermodynamics which states that if everything else is kept constant, then as a gas expands, its pressure decreases, and its temperature will also decrease. Likewise, as a gas is compressed, its temperature will increase.

This is because what we sense as temperature is really just a measurement of the amount of energy a molecule has. Simply put, if air molecules are bouncing around rapidly, then you would feel this air as hot. If air molecules are moving around slowly and sluggishly, then you would feel this air as cold. It’s that simple.

So what? This is important to understand because it forms the basis for how your air conditioner works. Your system works by allowing your evaporator coil to expand refrigerant inside of it, causing the coil to cool rapidly. As this rapidly cooled coil comes into contact with your home’s air (which your air conditioner blows over this now cooled coil), the refrigerant absorbs the heat from the air inside of your home.

1. Check your air conditioner’s air filter, if your AC is freezing up. This newly heated refrigerant is then transported outside of your home where it is compressed, causing it to heat up and transfer the heat that was once inside of your home to the outside air. The cycle then repeats itself over and over again, cooling your home in the process. For more information on the Joule-Thomson Effect, visit this page on Wiki: Joule-Thomson Effect.

Why is this important? Well because this effect is used to allow your air conditioner to cool the air inside of your house. But any time you change part of the equation, you might throw the system out of whack. So to keep this simple, your air conditioner is freezing up because something has altered your system in such a way that it is cooling your evaporator coil more than it should, causing the unit to freeze up. Now that you know how, what you have to do is figure out why your air conditioner is freezing up, and to do this you have to figure out what it was that threw your AC system out of whack. We will do this in the next section.

If you want to delve more into how exactly it is that your air conditioner cools air, take a look at: The Joule-Thomson Effect – Why Your Air Conditioner is Freezing Up, or just watch the video below:

Now that you have a basic idea of how your air conditioner uses expansion and compression to heat and cool its Freon (what is Freon?), you can figure out why your central air conditioner is icing up. Your air conditioner can freeze up for a variety of reasons, so we will discuss them from the most common to some of the more rare causes of ice up.

All of these causes are rooted in the Joule-Thomson Effect discussed above, so if you skipped past it, I’d recommend that you take a quick look or just watch the video above. Simply put, your air conditioner is freezing up because something is either causing the Freon in your system to expand more than it is designed to, which in turn is making your coils colder than normal, or something is preventing the air in your house from transferring its heat into your system. Either way, this causes your evaporator coil to drop below freezing and your air conditioner to freeze up. Here are some common causes:

1. Insufficient air flow across your air conditioner’s evaporator coil can cause it to freeze up.

In a split air conditioner (the most common type – see: What is a Split Air Conditioner?), our air conditioner is designed to drop the temperature of your house by taking heat from it. If your air conditioner is not properly blowing your inside air over the evaporator coil, then this heat exchange cannot take place and the Freon that should be removing heat from your home is not. Over time, its temperature will continue to drop and your air conditioner can freeze up.

2. If your air conditioner is low on refrigerant, then your air conditioner can freeze up.

This is due to lower pressure inside the system itself. This is because now there is less Freon in your system, but it is still being forced to expand the same amount – more expansion equals a cooler temperature. As your air conditioner’s evaporator coil drops below freezing, the moisture in your air will freeze as it comes into contact with your coil causing it to ice up.

3. Air conditioners are designed to function in a very specific temperature range.

If you are running your air conditioner when the outside air is below around 62 degrees, then the pressures inside of your system will drop and this can cause a freeze up of your central air conditioner.

4. Mechanical failures can cause your air conditioner to freeze up.

If there is a kink in your refrigerant lines, a blower fan that is not running or is dinged and out of balance, or a clogged filter dryer? These too can change the pressure in your system and make your central air conditioner freeze up.

But which is it, and how do I fix it? How to troubleshoot an air conditioner that is freezing up will be discussed in the next section. However, if you’ve already determined that it’s time to replace, make sure that you don’t overpay. This program will save you money, help you avoid the scams, tricks and traps of predatory contractors, and accept or reject bids with confidence:

Just because your air conditioner is freezing up does not mean that you have to call your HVAC contractor! Some contractors will tell you that they are the only ones that should touch your AC unit (I have never believed that), and if you don’t feel comfortable around your air conditioner then you should definitely call out a contractor. Either way, the first thing you need to do is turn your air conditioner off and allow it to defrost. Ice can harm your air conditioner! Next, if you do feel comfortable and if you have even a basic touch of the handy-man bug, then there are a few things that you should take a look at before you call your local air conditioning repair service. In order to troubleshoot a frozen air conditioner, I’d recommend you do the following steps in order: