Diagnose AC Unit Freezing

Outdoor AC unit
  • 1-3 hours
  • Intermediate
  • 0-500

Although most air conditioners see their heaviest use during the hot summer months, it is still possible for a central or window air conditioning unit to freeze up during these months.

Unfortunately, the solution isn’t quite as simple as just physically removing the ice in your AC system. To do so is treating the symptom and not the underlying cause, and it probably won’t permanently unfreeze your unit.

There are a variety of causes of this problem, all of which will dictate how you go about solving it. However, before you even begin to diagnose or repair the problem, the first thing you have to do is thaw the ice.

Step 1 - Thaw Ice From an Air Conditioner

To thaw an air conditioner unit, turn the entire unit off. Deactivate the breakers so the circuits do not short out during the thawing process.

WARNING: This is a very important step. The unit must be off and its breakers as well. Water and electrical appliances do not mix.

As the air conditioner thaws, water will drip and leak from the unit itself. To prevent the thawing water from creating a mess, fix a trash bag or bucket underneath the air conditioner unit. Monitor this carefully over the next couple of hours as the ice melts.

Once the ice has melted, allow the air conditioner unit to dry for 24 hours. Ensure the unit is entirely dry before operating it again.

Step 2 - Determine the Underlying Cause of the Freezing

person working on an air conditioning unit

There are several potential causes of freezing in an air conditioner unit. The filters, cooling coils, and fins all may be completely or partially responsible. In order to ensure your air conditioner does not continue to freeze in the future, examine each of these component pieces for maintenance needs.

Step 3 - Check AC Filters

Filters that are worn out or dirty may contribute to freezing in an air conditioner. Check to see if the filters are broken or need to be replaced. Typically, you should plan on cleaning or replacing the filters in your air conditioner unit every two to three months. Test them to ensure air can flow through them with ease.

Step 4 - Check Cooling Coil

The cooling coils in the air conditioner unit, also known as evaporator coils, are also potential contributors to freezing units. Essentially, the coil evaporates heat from the inside of the unit to the outside of the air conditioner system. By removing this heat, the coil lowers its temperature, and in conjunction with your AC’s coolant, this is the component that actually gets cold and allows your system to blow cool air.

Because of either poor airflow within the unit, which can stem from the filter problem mentioned above, or a lack of coolant, the evaporator coil can overcool itself to the point of creating condensation, which eventually freezes into the ice.

To treat the cooling coils, clean any dirt off of them carefully. As you do this, be careful not to bend any of the cooling fins that are attached.

Step 5 - Check Cooling Fins

hands at the front of an air conditioner

The cooling fins work in harmony with the evaporator coil. The fins are electric or mechanical. They are just physical structures that increase surface area for heat transfer within the unit. In the case of an air conditioner, the fins provide more surface area for heat to travel along and it moves away from the cooling coil and out of the unit and into the atmosphere. Assuming the fins aren’t broken, the best way to treat them is to use a vacuum cleaner to thoroughly clean the fins.

Examine the air conditioner fans to ensure they are working properly as well.

Step 6 - Evaluate Problems with the Air Conditioner’s Coolant

If you’ve ruled out other potential causes, it may be time to test the coolant levels, as this is a frequent cause of air conditioner freezing. Unfortunately many local regulations will not let an individual deal with refrigerant, and it may be necessary to contact a professional maintenance person or air conditioner technician to test and replace the coolant in your air conditioner. However, you can test and replace your air conditioner's Freon on your own, assuming local regulations allow it.

If any of these component pieces of the air conditioner do not seem to be functioning adequately, investigate whether they may be maintained at home or whether it is beneficial to hire an air conditioner technician. Thoroughly examining and maintaining your conditioner will decrease the chances of repeat freeze ups in the future.