air conditioner frozen

MrCool, Why is My Air Conditioner Frozen?

  • July 15, 2015
  • By MR COOL

Every summer some unlucky schlub wanders outside, slips on some ice, and says, “Hey! Why the heck is my air conditioner frozen? It’s burning up out here!”

Yes, it’s weird and completely counter-intuitive. How could ice build up on your air conditioner in the middle of a hot July?

Don’t freak out. It’s science.

So, Why is My Air Conditioner Frozen, Exactly?

Ice can build up on your air conditioner for two main reasons:

1. Low refrigerant charge.
2. Blocked airflow.

Let’s tackle each one like a Notre Dame linebacker.

Low Refrigerant

Air conditioners depend on super cold refrigerant in order to efficiently transfer heat from the inside of your house to the outside.  Ice can build up when that refrigerant gets too low. However, this isn’t the most common answer to the questions.

Airflow Problems

The main reason why air conditioners turn into ice machines is due to air flow problems. An air conditioner needs constant air flow to work properly. If that air flow gets interrupted or restricted, even by a dirty air filter, ice can start to build up on the coils. As you might suspect, a frozen air conditioner isn’t exactly the best way to keep your house cool in summer.

Fix the Frozen Air Conditioner Problem

So, how do you fix it? Follow these simple steps:

1. Cut the power to the air conditioner. It needs to be 100% OFF.
2. Let the ice melt naturally. This shouldn’t take too long in hot summer weather.
3. Make sure nothing is restricting the air flow around the condenser, the air handler, or inside your ductwork. If you find obstructions, remove or repair them.
4. Change the air filter, and make sure the evaporator coils are not too dirty. A filthy coil could have been the source of the problem.
5. Once the ice is all nice and melted (i.e. – completely gone), turn the unit back on.

Does it work? If it does, you’re probably okay. If it doesn’t, you’re going to need professional help. Contact an HVAC technician to get the unit serviced.


19 thoughts on “MrCool, Why is My Air Conditioner Frozen?”

  1. I installed my unit today and followed the instructions. An electrician connected the the unit. I turned it on and let it running for several hours. I noticed the unit was not cooling and the the low line was frozen. I need help troubleshooting. Everything is new.

      1. Hello my unit was installed today and my lines are frozen and aren’t cooling. I installed as per plans so I need help

  2. This is exactly what happened to us! It’s a brand new unit so I have no idea what could be wrong. The lines are not kinked and there’s nothing restricting the air flow.

  3. I have a 1200 BTU unit and today the small line is freezing up and the air handler inside is also seeing frost build up cleaned the coil and the filters. Getting the same results. Could this possibly be a leaking line or compressor going bad?

  4. My AC/Heatpump keeps freezing up when heating my garage. The outside temperature is mid 20’s and heating garage to 62 degrees F. I installed the 18000 BTU unit late this summer. There was no icing up (that I noticed) when cooling. What is your opinion as to what is causing the ice?

    1. Most likely the ice is caused by the below freezing temperatures. Condensation will build up on the outside coil during the heating cycle. On a heat pump, that condensate can freeze, and the unit will need to run its defrost to remove the ice.

      1. So the freezing up of the coils is normal operation? Mine is freezing up with temps in the upper 30s. It will go into defrost mode every hour or so. I don’t recall this happening last winter.

        1. At certain temperatures, the coil is going to freeze virtually no matter what. However, it shouldn’t be freezing in the upper 30s. That may indicate a low refrigerant level.

  5. Just bought a DIY 18000btu 20 Seer mrcool unit at Lowe’s. Had installer out yesterday to hook it up and install. Everything seemed to be working fine when he left. After a few hours on heat mode I noticed a lot of sweat or condensation on pad and unit outside. Was still heating good. Then the temp dropped to around 38 at about 9-9:30 pm and the fins outside were all freezing up. I turned unit off and talked to installer. What could this be?

    1. Ice build up coils can happen for a variety of reasons. Since you had it professionally installed, your best option would be to have the installer return to evaluate the system.

  6. i put one unit just couple of month ago a 3 ton central it freeze up to , try to heat up the house and have to put it in air conditioner to defrost it , is this normal run air conditioner in the winter i can’ t see other people or other unit doing this crazy thing we paid over 12000$ for this unit so what the problem this is not a joke

    1. An air-source heat pump condenser coil can build up ice in low temperature conditions. This will activate defrost mode, which does reverse operation (i.e. – turn on the air conditioning mode) to push heat into the condenser coil and melt the ice. This is a normal part of operation. It sounds like you need an auxiliary heat kit for emergency heating when your heat pump is in defrost mode.

  7. My new MrCool DIY 24K Outside Unit is encrusted with ice almost daily. I have a roof over it and the install manual directed amount of space for airflow behind and over it. I assume the automatic defrost cycle runs, but it doesn’t seem to fully melt all the ice each day. How can I activate Defrost Mode manually?

    1. Defrost Mode on a heat pump is basically just the Cooling mode, since that pushes heat out through the outside cool. For manual defrost, just switch the unit to Cooling. If you think your unit is malfunctioning, you can always call tech support at 270-366-0457.

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