Why Do Air Conditioners Freeze Up?

You’re in the middle of a heatwave when suddenly your air conditioning stops working. It can be a pretty scary moment when this happens, and there are a variety of reasons for it. Today, we’re focusing on one of the most common causes: a frozen AC. The air conditioner is one of the most essential appliances in every home. The last thing you want is for it to suddenly stop working because of freezing or damages caused by freezing.

How to Check If Your AC Has Frozen

A frozen air conditioning system can wreak havoc on your health and financial situation. Dealing with it can lead to serious air quality issues, which could make you very ill. If your cooling system freezes, you may need to replace the entire unit, and that can cost you thousands of dollars. Here are some warning signs to look for indicating that you have a frozen AC:

  • You set your thermostat lower than usual, but the temperature in your home is still warmer than you’d like.
  • Your air conditioning emits a strange noise.
  • You notice frost on your windows and/or on the outdoor unit of your air conditioner.
  • Ice accumulates around the cooling coils of a window air conditioner.

You can observe the ice buildup by opening up the AC panel. If you see no ice after checking the AC cooling coils, the unit can still have ice in it.

These flaws can dramatically affect your AC’s efficiency and your electric bill. Luckily, there are some simple fixes you can take to prevent this from happening. Check the following to make sure your AC doesn’t freeze up:

A Clogged Line

If you find that you have a clogged condensate drain line, you could be facing a larger problem. Having clogged condensate drain lines causes the air conditioner to hold on to more water than normal. If the temperatures dip below 32 degrees, the trapped water will cause the evaporator coil to freeze. The result? You’ve got a refrigerator-sized box of useless metal instead of a well-regulated environment.

Low Refrigerant Level

If your air conditioner is freezing up, first check the refrigerant level and make sure it hasn’t run out. If it has, you’ll need to have the refrigerant topped off before the air conditioner will work properly. Call one of our technicians to add refrigerant to your AC.

Dirty Filter

One of the most important things to do to keep your AC running smoothly is to make sure the filter is clean and changed monthly. This will help reduce your cold air costs and keep your air conditioner running efficiently.

Supply Vents

Partially or completely closed supply vents can also be the cause. You need to keep the supply vents open. This will help keep the air moving and prevent your AC from freezing.

Cold Coils

The cold coil of an air conditioner must stay warm. Otherwise, the condenser coil will freeze up, and there will be a risk to the compressor. There are several ways to keep the cold coil warm, even though some are more effective than others. Call our technicians to help with this issue.

Fan Speed

The AC unit will freeze up when you don’t set the fan correctly. If you set the fan to a low speed, the air entering the HVAC unit will be cold and cause it to freeze up. To avoid this from happening, increase the fan speed to allow warm air to enter the HVAC unit.

Defrost Board

Most modern AC units come with a defrost board. This board helps it recognize when ice is forming on the coils. When this happens, it turns on and double-cycles for a few minutes so that it can melt the ice off. These outside units work fine, but if you start to notice ice covering the inside evaporator coils, there is a communication issue between the defrost board and the air conditioner.


If you set the thermostat too high, it can restrict the airflow, resulting in poor air circulation. This will cause condensation and freeze your unit from inside.

Condensate Drain

You must inspect the condensate drain weekly to make sure it’s clean. A clogged condensate drain will cause the system to freeze. It’s important to note that a blocked condensate drain can also lead to other issues within the system.

Window Angles

One of the most common mistakes we encounter with window units is that people angle the AC wrong. It is important to make sure that you install your window air conditioners right. Angle them correctly to ensure that they won’t cause a bigger problem when they freeze up.

Metering Devices

The TXV (Thermostatic Expansion Valve) is an expansion valve used in the liquid line of an air conditioning system. We find this regulating device in most air conditioning and heat pump systems. It has a built-in thermostat that will control the amount of refrigerant sent through the coil so that it can pull excess heat out of your home.

If you’re experiencing problems with your AC unit, a faulty TXV valve could be the cause of it. It can become unresponsive to the signal and allow refrigerant into the evaporator coil, which causes it to freeze.

Solutions to Defrosting a Frozen AC

The best advice for defrosting your AC is to seek out help from a professional. The longer you wait to defrost, the more damage it will do to your unit. Your cooling system works on many little moving parts, and every single one of them can affect the efficiency of your AC. An expert will service your system to make sure all of those parts are frost-free and in good working order.

HVAC Services

An HVAC professional can do several things to ensure your cooling system stays running at peak performance. Our technicians can perform a refrigerant leak test, change out your condenser and compressor, replace your circuit board or do a full system tune-up. Each procedure is necessary for eliminating any deficiencies that might cause technical issues for your home cooling system.

Schedule Regular Maintenance

In order to make sure your air conditioner never has a frost problem again, schedule regular maintenance. By having your air conditioner professionally inspected and cleaned regularly, you can help it remain in top condition and get the most from it. You won’t have to worry about a frozen AC or any other issue going undetected.

Award-Winning AC Repair Services in the Greater St. Louis Area

Since 1983, our family-run business has been providing excellent services for your cooling and air quality needs. We offer complete solutions for all of our customers in O’Fallon and the surrounding areas. Whatever it is, we’ve got you covered. Whether it is installation, maintenance, unit defrosting, heat pump repair, or air cleaning, our trained technicians will do whatever it takes to keep your AC running smoothly with minimal downtime. We also offer revolutionary technology for indoor comfort solutions. To protect your family, save money on your energy bill, and extend the life of your unit, call Hoff Heating & AC today.