How bizarre! It’s 100 degrees in the shade, and you’re wondering why your house is getting hot. You head outside and see that your air conditioner is freezing up.

How can that be?

Actually, it’s fairly common. But yes, still bizarre. How could such a thing happen?

It could happen for several reasons. It could be your filter—because any problem can be due to the filter! Or it could be something serious like a refrigerant leak.

I’ll provide a complete list below, plus possible solutions—if there are any. So read on.

8 Reasons Why Your Air Conditioner Keeps Freezing

Let’s start with the simpler things—or at least things you should be able to troubleshoot and fix yourself. Then I’ll move on to issues that will likely need a pro to fix.

Your AC Could Freeze Up Due to . . .
Dirty Air Filters
Dirty Air Ducts
Bent or Dirty Condenser Fins
Closed or Blocked Vents
Refrigerant Leak
It’s Cold Outside
Blocked Condensate Line
Damaged or Dying Blower Fan/Motor

1. Dirty Air Filters

dusty air filters
Make sure to clean or change your filters regularly

For such a cheap part—at least in comparison to your other HVAC equipment—the air filter can cause all sorts of problems.

Actually, it’s not the filter. It’s homeowners not doing regular maintenance and changing or cleaning the filter.

The filter’s job is to catch particles in the air before they enter your ducts and ultimately pass by your blower. Because the debris can destroy the blower motor. However, if left unattended, that same filter can also destroy your blower motor.


Because as dirt and debris build up on the filter, it blocks airflow. That means your blower motor now has to work harder to move air through the filter. Ultimately, condensation starts to build up on the evaporator coil.

The evaporator coil has a cold surface to the condensation starts to freeze.

If you don’t change out your filters, the buildup of ice just keeps building up.

Solution: Change your filters! Depending on your system and your filter of choice, this may need to be done every three months. Maybe less, maybe more.

2. Dirty Air Ducts

dirty air ducts
Ducts need care and attention too.

Who hasn’t got the air duct cleaning telemarketing spam call a time or a hundred?

Most of the time you can just hang up, secure in the knowledge you don’t need your ducts cleaned.

However, there are times they may need to be cleaned.

  • Have you recently done any sort of reno or construction in your home?
  • Do you have a big family with lots of kids, pets, and dirt?
  • Have you just moved into a resale home?

Just as dirty filters will impede airflow, so will a buildup of dirt in your ducts. Again, this will eventually cause your evaporator coil to freeze up.

Solution: Construction typically leaves a lot of dust behind, and that will find its way through your ductwork.

Big families and pets can create a lot of dust and debris, so cleaning your ducts every 3 or 4 years may not be a bad idea.

If you’ve just moved in, you have no idea when they were cleaned the last time, if ever. So getting them checked and cleaned is just a smart idea.

3. Bent or Dirty Condenser Fins

Yes, dirt is the culprit yet again.

If too much dirt builds up on the fins of your condenser, it can’t absorb enough heat from the air. This causes a condensation buildup, which in turn causes an ice buildup.

The same thing can happen if the fins get bent.

Since your condenser is sitting outside, unprotected from the elements, it can get hit by hail, blowing branches, and anything else heavy enough to damage them. Even toys and balls.

Also, your condenser isn’t to be used as a prop for things like your bicycle. Anything that can damage the fins should be kept at a distance.

Solution: Before you start cleaning, make sure to turn to power to your AC off. You’ll either have a breaker outside near your condenser or you’ll need to shut off the breaker at your main panel inside.

  • Clean around the outside of the unit and then remove the top grate carefully. The fan, and perhaps the motor as well, is attached to it.
  • Remove any dirt that has collected at the bottom, either by hand or with a shop vac.
  • Inspect for damage to the fins. Some may be bent, so they should be straightened out.

For those of you who prefer visual instructions, check out this video.

4. Closed or Blocked Vents

When we talked about filters—and even the condenser—the problem caused by the buildup of dirt was reduced airflow.

Guess what? Putting the sofa in front of a return air vent or closing a supply vent off can do the same. Every system has specific airflow requirements. When it doesn’t get what it needs, bad things happen. Expensive things happen.

Solution: Don’t block return vents. They’re typically on a wall, not far from the floor, so this might be a challenge. But they are not supposed to be blocked.

Don’t close your supply registers all the way. They’re fine to partially close but allow for some airflow.

Turn the thermostat to the off or Fan setting, make sure all your grates and vents are open and accessible, and wait until the coil thaws out. Once the ice is gone, you can try partially closing a supply vent or two to see if it starts to ice over again. If it does, you have your answer. You need to keep them open.

5. Refrigerant Leak

Has the ice formed on the side panels of your AC unit? Then you could have a leak. The second thing you might notice is a hissing sound.

Solution: This isn’t something the homeowner can deal with. Only certified technicians are legally allowed to deal with refrigerants.

6. It’s Cold Outside

cold weather outside house
Sounds silly, but make sure not to turn on the AC when it’s cold out!

Have you lost your mind and put the AC on when the outside temps are less than 62 degrees F / 0 C? This will cause a pressure drop and may cause any condensation to freeze.

Solution: If it’s winter, and your house is hot for some reason, open the windows. Do not turn on the AC.

7. Blocked Condensate Line

The condensate line runs from your indoor unit to your outdoor unit. It’s often a PVC pipe and its job is to remove condensate away from your HVAC. However, if it gets clogged, water will sit in it and it can cause your coils to start to freeze over.

Solution: It’s a good idea to clean your condensate line at the beginning of every season. You can use bleach for that. If you have a block, you can use a shop vac or drain snake to remove the clog.

8. Damaged or Dying Blower Fan/Motor

It’s not common, but your blower fan can break. Or your motor can break down if filters are so dirty it must work harder. Of if you’re using a high MERV filter when you shouldn’t be. Again, this will cause your motor to work harder and often burn out.

Problems with either the fan or the motor will impact airflow, which can cause your AC to freeze up.

Solution: If your fan is noisy, or not running at all, you’ll need to call a technician to inspect your system.


It might seem bizarre to see your AC frozen over in the heat of summer, but as detailed above, there are several reasons why it could happen.

  • Dirty air filters
  • Dirty air ducts
  • Bent or dirty condenser fins
  • Closed or blocked vents
  • Refrigerant leak
  • It’s cold outside
  • Blocked condensate line
  • Damaged or dying blower fan/motor

In most cases, there is something you can do to stop it from happening again, but in some cases, it will mean a call to a pro and perhaps a large bill to get it fixed.

The best thing to do is keep up with your maintenance—and don’t close or block vents. Follow these instructions, and you should be fine.

Hopefully, you found an answer to your question here. Why not check out our related topics and articles below?