Today I noticed the AC wasn't working. I checked the unit outside and saw the line freezing. I checked inside and it's frozen as well.

I turned the AC off and fan on. The ice is melting now.

I suspect it has to do with poor air flow. I bought this house 3 months ago and the pleated air filter was missing. I put one in and the AC continued working fine. It stopped working one time a few weeks ago. I turned it off for a bit and back on and it worked again. I didn't think much of it.

After the ice melts, what should I do before trying to turn it back on? I'm going to clean it as best I can. I'd like to avoid further damage and calling a professional.

This is inside the house. Looking up into the AC. Normally there is a pleated filter coving this but I removed it to see: This is inside looking up into the AC. Normally there is a pleated filter over this but I took it out.

This is right below the above picture. The ice is melting into the buckets: enter image description here enter image description here enter image description here enter image description here

Edit: After the ice melted. Hard to tell but I cleaned it using a mop. A lot of dust fell from it. I turned it back on and it's working well so far.

enter image description here

enter image description here Edit: Same issue happened again. Had to call an AC repairman for $135 to add refridgerant.

  • The first picture is obviously something thoroughly iced over. What is that and where in (or out of) the house is that? Otherwise, very well presented question!
    – FreeMan
    Commented May 28, 2020 at 17:47
  • 1
    Thank you. I'm updating. Commented May 28, 2020 at 17:55
  • 1
    running it w/o a filter probably coated all the important bits with dust; you're on the right track.
    – dandavis
    Commented May 28, 2020 at 18:37

1 Answer 1


There are a few causes for this, and the most common are in two categories - bad air flow and low refrigerant.

Bad airflow can be caused by a dirty filter, clogged ducts, or a poorly performing fan. If the (relatively) warm air from your house isn't blowing over the coils, the condensation they normally create starts to freeze. Once they start to freeze, airflow is reduced, the coils get colder, and even more ice forms.

The other common problem is something a technician will have to check. It sounds counterintuitive, but low refrigerant can end up making the coils too cold. The results are the same runaway reaction described above - lots of ice, reduced airflow, and a compressor that never stops because the house isn't getting cooler.

Once the system thaws, check all your filters and make sure the blower fan works fine. You can check the coil temperatures with an IR thermometer while the system is running. If it gets below freezing and airflow seems good, it's probably time to call a tech.

  • Problem happened again. Why would I have to call a technician? How can I check for low refrigerant? Should I clean the airducts? The fan on the outdoor unit looks like it's running fine. The air above the fan is cool. Commented Jun 4, 2020 at 16:31
  • The outside unit is for getting rid of heat. The air above it should be warm. Of course, the blowing of the air might make it seem cool, but it should normally be warmer than the surrounding air because the compressor creates heat. You can't check the refrigerant level without the proper specialized and expensive equipment and the knowledge to use it. Cleaning the air ducts wouldn't fix or cause this problem.
    – JPhi1618
    Commented Jun 4, 2020 at 16:35

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