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.


47 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. Is it unusual for the ice to remain on the fins without ever completely defrosting. My unit goes into defrost mode at times, but it doesn’t seem to do this when there is frost on the fins. Also, the bottom fins never accumulate any amount of frost. The function doesn’t seem to be adversely affected, but I do notice that air flow seems to only exist around the perimeter of the fan, and not directly in front of the unit.

      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.

  8. My heat pump is 3 years old. I found about 1/2 inch ice on the pad. None on the coils or condenser. Please help , is this urgent to keep it working? Its currently 24 degrees with temperatures dropping in the next few days.
    Thank you

    1. If you’re running the heat pump in heat mode, that ice buildup is probably from condensate freezing on the pad. Unless you’re experiencing a problem with the heating function, it shouldn’t be an issue.

  9. I just installed a 3-zone unit and one of the handlers started splashing water and the line to the condenser for that particular handler is frozen. Can someone advise?

  10. I installed a 4 zone unit. All electrical was done professionally. I hooked up the line sets and checked for leaks with soapy water. One indoor unit is dripping water even when it is not on. The connections at the outdoor unit are covered with ice. When thawed out and checked for leaks with a leak detector nothing was found. What is making the one unit one the inside drip water like it has ice in it thawing. Like I said it’s not even turned on. And by the way the system is only about 3 months old. Thanks

    1. If your unit was professionally installed, your first recourse should be to have the installer come back to review their work.

        1. If you have a DIY that is dripping water, it is likely not level or the drain hose is clogged.

  11. We have a Mr Cool model A12 HP-C-230A. It started freezing up about halfway through summer last year, after only 3 months use. I turned it on again today and the ice starts to form on the outside line immediately. Obviously this is a major issue with Mr Cool HVACs. My question is; What is the company going to do about it? I don’t think I should have to absorb the cost of repair on a unit that we got so little use out of.

    1. Since you’re using our Advantage model that requires professional installation, you should contact the local professional you used to check that there was not an issue with their installation work. If it was installed correctly, they can contact us on your behalf for a warranty claim.

      1. I have a 3 week old diy 27k 3 zone that is acting like described above from day one. It only freezes up when I have one zone on. If I turn on another handler the lines are fine. Is that normal?

        1. To ensure that your unit is operating as it should, the running air handlers should equal at least half of the capacity of the condenser. For example, if you have a 36k condenser, and you run a single 9k air handler, the unit will likely not operate properly. If this is not the issue, please give us a call at 270-366-0457 as soon as you possibly can.

          1. Thanks, this is reassuring. It sounds exactly like the issue, because it works totally fine when I run the second. Appreciate the quick response. Hopefully this helps others in this thread. Nice product so far. I have some other questions but may be easier to call. Thanks again.

  12. I have a 2 zone mini split MRCOOL unit. One 9 k and the other a 12k. This is a DYI unit so it was installed by me. All electrical was done by a license contractor. My outside Lines freeze up after about an hour of use. Also my king valve freezes up as well. In your directions you say to open up this king valve which I did. When the lines freeze up the AC stops working in my living room unit but the bedroom unit is cold and I cannot seem to turn it down to a comfortable level and I found ice in the filter?? What’s wrong? Is my outside unit to strong for my two indoor units a 9 k BTH and a 12 K BTU? I spend 2400.00 buying this unit and followed all your instructions. Please let me know what else I can do. Oh and I also did the mother board button push that did not work either. HELP!!

  13. Seems I am having the same issue with my unit. It’s brand new, only been installed for 5 days. It a 2 zone diy system. I connected everything according to the directions and checked lines for leaks. I had a licensed electrician do all the electrical. One of my units is working (not very cold air but not frozen) the second unit is frozen, inside head is full of frost and ice and lines are frozen all the way to condenser. No issues with air flow, and the filter is completely clean.

  14. Bought the 4-5 ton universal series around November 2020. Has worked great. Yesterday I came home and the condenser was running, but the air handler was not. There was power to both legs, I can hear the Freon and feel the line and coil get cold, but the fan never kicks on. Any help would be great. And yes, I did check and replace filter to make sure it was not an obstruction

  15. bought and installed the 4-5 ton Universal Series unit around November 2020. Everything has worked fine, except yesterday, one of the warmest and humid days we’ve had in a while, it stopped working. When I got home from work the condenser was running, and there was a small buildup of ice on the coil and inlet line, but the blower never kicked on. I checked the filter, which was ok, but replaced it, checked to make sure the breaker for the air handler was good, and checked at both legs which also had power. Even hours after what little ice had melt, still not running

  16. I have a 4-5 ton universal diy heat pump. I was told to buy this unit since my house needs about a 3.5 ton unit. I have the switches set to 4 ton. When the unit turns on cooling, it has a minor burn (unique and distinct) smell for the first minute or so, then all is well. We cool down to about 74-75 and have zero issues, but as soon as I set it to 72-73, the exposed parts (connection points) of the r-410 lines freeze up and the A-coil does also. I have the mrcool thermostat that the tech department said didn’t have wifi capability working correctly, nor the App. I can’t seem to figure out the Thermostat, so I set it manually. I was told to wait until the weather gets cooler because I haven’t been able to test un the heat here in north florida because September was very hot outside. I changed the filter as soon as I was having issues and the filter wasn’t that dirty. Any thoughts on what the problem could be?

  17. Hi i live in Vermont and i purchased the 4-5ton heatpump house is around 3000sq ft i switch it to 4ton should i keep it at 4ton or switch it back to 5ton what are the benefits keeping it at 4ton vs 5ton and we only use it for heat.

    1. Square footage alone is not sufficient for determining the btu requirement for a specific house. With adequate ductwork, I would suggest trying the 5 ton settings first. If that works without short cycling, then it should be fine. Should you experience short cycling, the settings on both the indoor and outdoor units can be reduced to the 4 ton setting.

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