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Why is my air conditioner freezing?

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Last Updated on April 26, 2019


air conditioner freezing up | ac unit freezing up

You may expect your air conditioner to be cold, but if it’s covered in frost or ice, that’s not a good sign. When your air conditioner is freezing up, it can’t properly cool your space. And worse, if you don’t do something about it quickly, you can end up with water damage in your walls and ceilings as well as an expensive AC repair on your hands.

There are a number of causes for an AC unit freezing up, but the most common are:

  • diminished airflow, due to anything from a clogged filter to a broken fan
  • an obstruction in the drain line
  • a refrigerant leak
  • a faulty thermostat

Most of these causes of an AC unit freezing up are readily fixable if you catch it in time. However, if you ignore an air conditioner that’s freezing up for too long, the strain on the system can lead to compressor failure. That’s a very steep repair cost at best, and might mean you need a new air conditioner.

What to do when your AC unit is freezing up

If you notice that your air conditioner is not cooling well, and you take a look at the indoor unit and see ice or frost on the coils, the first thing you must do immediately is TURN THE UNIT OFF. Don’t just turn up the thermostat temperature setting; set it to OFF.

The longer it runs when the air conditioner is freezing up, the more likely you’ll end up with permanent compressor damage.

How to unfreeze your AC unit safely

If there is a great deal of ice on the coils, you might not want to wait for your AC service technician to remove the ice. Depending on where your unit is located, the melting ice can drip causing water damage to your floors, walls and ceilings.

Related article: Why is my AC leaking water inside the house?

If you are worried that this might happen, you need to know how to safely remove the ice without causing further harm to the equipment. IMPORTANT: Never use a sharp object to try to chip away the ice, which can cause damage to your air conditioner’s sensitive coil fins!

Try these techniques instead:

  • Try turning on the system fan (turn the thermostat to the FAN setting so the AC is not running) to melt the ice. This may take a few hours. IMPORTANT: Don’t try to do this if there is ice on the fan!
  • If the fan is not working (or you want to melt the ice faster), you can try using a blow dryer to melt the ice.
  • If it looks like the melting condensate is dripping outside the drain pan (or even into the ducts), use a wet vac to clean up the water. The last thing you want is water in the ducts that can lead to mold growth.

While you’re at it, you might want to check the condition of your air filter. If it’s completely clogged, that might be why your air conditioner is freezing up. To function properly, your AC needs warm air flowing over the coils. A clogged filter reduces the air flow, and can result in the AC unit freezing up. Changing out the filter might be all you need to do to solve your problem.

Related article: Why and how to change an air filter

If it’s not the air filter, though, it’s time to call in an HVAC expert to get to the bottom of your AC unit freezing up.

Call in the pros to diagnose the cause of your frozen AC unit

At this point, your air conditioning problem must be diagnosed by a professional. If you didn’t find a clogged filter, never melt the ice and turn the unit back on without an inspection! That’s because of the possibility of refrigerant leaks, which is a problem you can’t fix on your own. If you have a leak (or multiple leaks), you’ll see the air conditioner freezing up again. And this time you might burn out the compressor.

Here are some of the problems that might be uncovered.

Fan problems. If you tried to melt the ice with your system fan and it failed to turn on (or seemed to be running sluggisly) this could be the culprit behind your air conditioner freezing up.

Again, it’s about a lack of air flow. If the fan doesn’t run, there’s little air flowing over the coils and they get too cold. In this case, your technician will probably need to replace electrical components or the fan motor.

Faulty thermostat. Did you notice that your air conditioner seemed to be running constantly when the temperature wasn’t that high? It’s possible that your thermostat is not sending the proper signal to tell the AC unit to turn off. Running constantly also causes the coils to get too cold, and leads to the air conditioner freezing up. Your thermostat may need to be recalibrated or replaced.

Refrigerant leaks. Refrigerant is the chemical that runs through your AC coil, changing pressure and temperature in order to remove heat. If refrigerant leaks develop in the lines or the coils, the reduced pressure will result in the refrigerant lines, and then the coils, freezing over.

Here’s an important fact to know: your AC system does not consume refrigerant. It’s a closed system, and you should never need to add refrigerant unless there’s a leak. So, if you’ve been told you need to add refrigerant to your system every year or so, then you have a leak that must be found and fixed.

If you do have refrigerant leaks in an older system (installed prior to 2010), there’s an even more important thing you need to know. If your system uses the refrigerant R22 (also known as Freon), that refrigerant is being phased out as per the EPA as of January 2020. Even now, it’s becoming very expensive to obtain. What does this mean for you? Right now, it means a much more expensive fix for your air conditioner freezing up. In the not-too-distant future, it means you’ll need to replace your air conditioner.

Learn more here:

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AC unit freezing up: preventative measures

Many causes of an air conditioner freezing up are preventable. That’s because they start with a small problem that leads to a bigger one. You can nip those small problems in the bud with yearly preventative maintenance. Having your system inspected, cleaned and tuned up can prevent airflow issues and even refrigerant leaks by keeping the coils clean and corrosion-free.

Find out more: Q&A about HVAC Preventive Maintenance Contracts