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Why Are the Coils Frozen on My AC Unit?

A white kitchen with flowers on the table

If your AC seems to be cycling on and off more often, running longer, blowing warmer air or in general not working well, it’s time to investigate. The sooner an AC problem is fixed, the better. When an AC stops working, it’s not only uncomfortable and inconvenient; it can be downright dangerous. When your AC malfunctions, you may wonder, “Are the coils frozen on my AC unit?” If you fear you have a frozen evaporator coil on your AC unit, it should be diagnosed quickly to avoid bigger and more costly problems.

By now, you might be wondering, what is an evaporator coil and what does it do? The evaporator coil is the part of the air-conditioning system that absorbs heat from the air inside a house. It is a series of U-shaped tubes filled with refrigerant and connected to the indoor components of the AC system.

Depending on the AC system, the evaporator coil may be near the air handler or inside the blower component of the furnace. Evaporator coils work to cool your home by pushing warm air inside your home over cold coils. The air cools and the refrigerant inside the coils gets warmer. Then, the warmer refrigerant is transported to the outside AC unit condenser coils.

Here are some common signs that the evaporator coils are frozen on your AC unit:

  • Warm air is coming out of your indoor AC vents, even when you set the thermostat to a cooler temperature.
  • The AC keeps cycling on and off, but the house isn’t cooling.
  • When you turn on the AC, nothing happens.
  • The AC system is making pulsating noises, or banging or hissing sounds.
  • There’s a leak near your AC’s indoor components. This could be caused by ice from the coils melting into water and overflowing out of the AC drip pan.

Evaporator coils freeze when they aren’t cleaned and maintained and get covered with excess dirt and debris. Clogged air filters also lead to frozen coils, which is why it’s so important to change your AC filters at least once every three months. A refrigerant leak can also lead to frozen evaporator coils, as can a broken blower within the system. These conditions force the AC system to work harder to do its job, leading to frozen coils.

If you know you have a frozen evaporator coil, it’s a good idea to turn off the AC so the problem doesn’t get any worse or cause further damage. Contact a licensed heating and cooling specialist who can diagnose the AC problem and recommend the best way to fix it.

water leaking fro an ac unit with a dirty evaporator coil

Problem: Dirty Evaporator Coil

When your AC isn’t working well, there are several possible reasons for the problem. A dirty evaporator coil is one of the most common AC issues. Signs include an AC that’s blowing warm air instead of cold, there’s water leaking from the unit or there’s excessive moisture and condensation on the indoor components. A dirty evaporator coil can become a frozen one in no time, and frozen evaporator coils can turn into even larger issues.

The evaporator coil cools your home by removing heat from the air inside and transferring it to the refrigerant that runs through the coils. If the evaporator coils are covered in dust and dirt, they have to work harder to draw heat from the air. Dirty coils can put a strain on your whole AC system and cause the evaporator coils to become packed with frost and ice.

Depending on the type of AC system you have, the evaporator coils may be inside the furnace blower compartment or the air handler. AC components are usually located in the attic or inside a crawl space in your home, which means most evaporator coils aren’t easily accessible. Also, AC components carry voltage and involve moving parts, these parts of your AC system can be dangerous to work with if you aren’t sure what you’re doing. Furthermore, frozen evaporator coils are sometimes caused by refrigerant leaks. Refrigerant is toxic and harmful to the environment.

How To Prevent Dirty Evaporator Coils

Since many of us don’t know exactly how HVAC systems work and how to best maintain them, dirty and frozen evaporator coils are AC problems that are best left to a professional. A licensed AC specialist will have the tools and training necessary to diagnose problems accurately.

It is best to contact a professional when you’re having problems with your air conditioner. There are also steps you can take to prevent AC issues from developing:

  • Change out your AC filters routinely, or clean them regularly if you have reusable filters. Once every three months is a good rule of thumb, but you may need to change your filters more often if you have pets that shed, spend lots of time outdoors or have other factors that contribute to a larger than average amount of dust and dirt in your home. If your filters are incredibly dirty, they’ll cause low airflow within the AC system, leading to frozen coils.
  • Upgrade to higher-quality air filters. Investing in better quality filters can go a long way toward preserving your AC system and extending its life over time.
  • Hire a reputable AC specialist to service your AC system every year. Regular maintenance can extend the life of your AC system. An AC specialist will clean and inspect the entire AC system, and run refrigerant checks and other tests to make sure everything is working properly. Regular AC maintenance checks can help AC professionals spot problems before they develop into major, costly repairs.

a living room and kitchen

Problem: Replace Evaporator Coil or Whole Unit?

When your AC isn’t working well because of a bad evaporator coil, you might run into a common dilemma: Should you replace the evaporator coil or the whole AC unit? Before buying a new AC unit, you should consider many factors, including the particular issue with your evaporator coil, as well as the age of your AC unit. Most AC specialists recommend replacing the entire AC unit once the evaporator coil becomes worn down. If your evaporator coil has gone out and your AC unit is older, you may have other problems along with that bad coil.

Evaporator coils wear down from corrosion on the outside of the tubes and erosion on the inside of the tubes. As the metal coils weaken, they become vulnerable to refrigerant leaks. The refrigerant within your AC shouldn’t ever leak, given that it’s within a closed system traveling through tubes between the AC’s evaporator coil indoors and its condenser unit outside. The only time refrigerant can leak out of tubes is when there is a major problem with the unit, for instance when evaporator coils have broken down.

So when your AC’s evaporator coil goes down the tubes, should you replace the evaporator coil or the whole unit? In some cases, it may make sense to replace the coil, for instance, if the AC unit is newer—less than eight years old—and it runs on a newer AC refrigerant. Yet, in the majority of cases, it’s wiser (and more cost-effective) to replace the entire AC unit.

The average lifespan of a typical AC system is 10 to 15 years, so when the evaporator coil starts to fail, it’s often because the entire unit is failing. The unit may have many problems, not just a bad coil. The evaporator coil needs to be a good match for the condenser, and it often isn’t possible to make a good match when replacing these parts on an older AC. The evaporator coil works in conjunction with the condenser coil, which is located in the outside unit. When the evaporator coil goes bad, a new coil might not be compatible with the old condenser.

Another reason to replace an entire AC unit is if it’s an older unit that uses R-22 refrigerant, more commonly known as freon. R-22 was the refrigerant of choice in older AC systems until it was determined to be harmful to the environment. Since 2010, there has been an effort to phase R-22-dependent AC units out. Newer AC models are made with a safer alternative refrigerant, and R-22 hasn’t been produced or imported since 2020. If your unit uses this phased-out product, it’s best to replace the whole unit when the evaporator coil goes bad, given the difficulties in obtaining R-22 refrigerant and the movement to drop units that use it.

If you are having issues with your AC unit, finding the source of the problem can be involved and time-consuming. Contacting a licensed heating and cooling specialist can take the guesswork out of it and save you time and money. Let an AC specialist diagnose your AC problem, answer any questions you may have and recommend the best way to resolve it.

ABC Can Get Your AC Unit Running Smoothly Again

It can be tough to diagnose your AC unit on your own. Instead of trying to fix the problem yourself, contact ABC Home & Commercial Services. Our licensed specialists are highly trained. They can get to the root cause of your problem and then make all AC repairs. This way, you and your family members won’t have to worry about your AC malfunctioning or not working at all.

Tom Riggs

Tom Riggs is the Division Manager for Mechanical Services, overseeing sales and operations for HVAC, Plumbing, Electrical, Appliance Repair and Water Quality for all ABC Austin branches. He joined ABC in 2014. Before ABC, he was an HVAC Service Technician, HVAC Comfort Advisor/Sales and Operations Manager. Tom attended Universal Technical Institute. He's an avid outdoorsman and enjoys country living with his wife and two sons.

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