If it’s winter where you are and your AC seems to be acting up, chances are the answer to the issue is that the AC is freezing up. Diagnosing the issue is the first step, figuring out what’s causing the freeze up and how best to tackle the issue requires a little bit of research and knowhow to tackle. Below we have a guide for how to deal with an frozen AC unit.

How Do Window Air Conditioners Work?

In short, the main job of your window unit AC is to get the air moving in the room. It does a lot more than that, but the first step is getting the static air in a room moving. When the AC kicks on, the compressor and coil immediately start working together to drop their temperature. While this happens, the blower starts to pull in “room air”.

The first stage of room air in the AC unit is the separation of dust and other particles from the air. Then the air travels through the cooling coil (also called an evaporator coil). The temperature of the coil against the temperature of the room air allows not only for the temperature of the air to drop, but it also removes moisture from the air resulting in the dew collection in the unit. The AC’s blower then takes the air through the rest of its journey where it is “exhaled” back into the room, cooler and without humidity.

What Causes Air Conditioner Units to Freeze Up?

As you might imagine from the several steps in the air cooling process, your air conditioning unit has many parts and, as a result, a freeze up of the unit could be linked to any one of several culprits. But, what it ultimate comes down to is restricted airflow. There’s several places that the airflow can get jammed but, at the end of the day, clogs in the flow of the unit will cause a freeze up. AC units are designed to function in an optimal temperature above 62, anything below that and certain blockages can start to happen.

Airflow could be blocked at several points in the machine. There’s some fun physics involved that essentially boils down to: temperature drops when molecules still.

  • When airflow is blocked the evaporator coil will start to frost.
  • If the refrigerant is low, the entire machine can freeze up.
  • If the air around your unit gets below the designed temperature above, icing on the unit can occur as well.

While weather and season can be a factor, most of the time a frozen air conditioner unit goes back to a mechanical issue that disrupts the airflow. Luckily, there are plenty of ways to diagnose the problem if it is mechanical, and plenty of ways to try and DIY a fix before you’ll want to call in a professional.

How to Fix AC Freezing Up

Check the air filter

This is the first place to look because it’s the most common place where blockages start. If it’s clogged, you’ll need to replace it. In order to avoid a blockage in the air filter in the future, make sure you’re using a high quality filter and replacing it every 3 months.

Check evaporator coil

The evaporator coil is an important part in the air cooling process. Since it pulls moisture out of the air, it can become dirty and clogged, restricting airflow and causing the unit to ice over as the temperature becomes unstable. It can also cause the secondary problem known as “Dirty Sock Syndrome” as bacteria builds up, emitting a foul smell when the unit is turned on.

Check for any restriction in the air ducts

If the unit itself seems to be working properly, you’ll want to turn your search towards the ductwork connected to the unit. If you do find a blockage in the ductwork, it is in your best interest to replace the ductwork, rather than try to clean it out since cleaning the ductwork can be expensive and even damaging to the ducts.

Check for dirt that may be blocking ducts

You may get lucky and find the duct block is much more accessible than you thought. It’s possible there’s a build up of debris at the entrance to the ducts, blocking the air. It’s easier to manage than a full cleaning or a replacement of your ductwork.

Determine if you need to replace your unit

If none of these places reveal the cause of your frozen AC unit, then you’ve gone as far as you can without calling a professional. It may be time to bring someone in to diagnose it and time to get yourself a new AC unit. Depending on the issue an HVAC pro might be able to salvage the unit. You could have an issue with low refrigerant, too much refrigerant, problems in the refrigerant lines, mechanical problems in the fans, or a number of other, more in depth, issues. Once you get a quote from a pro, you’ll need to consider if working on a fix on an older unit is worth more than simply getting yourself a new unit. On average, you should expect to pay around $7,000 for a new full unit with labor and fees.


An air conditioner freezing up is frustrating, and sometimes it’s an easy fix. But sometimes it’s more complicated, perhaps even more than one issue. You’ll first want to take a look for yourself to see if you can diagnose the issue. Once you do, determine if you need a pro to perform a fix, and, if it comes to it, know when it’s time to trade out an old, frozen unit for a new one. If it’s time to call a pro, head over to eLocal to find the right HVAC pro for you.

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