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My Air Conditioner is Frozen! What Caused This to Happen?

By September 26, 2020June 17th, 2024HVAC
What caused my air conditioner to freeze up?

Living in the south, air conditioning is essential.  Temperatures are at the levels where the air needs to be turned on most months of the year.  The air conditioning keeps us cool by removing the heat and moisture and allows us to be able to escape the outside temperatures comfortably. 

In most homes, the air conditioning unit is outside and called the HVAC- Heating, Ventilation, and Air Conditioning System. This unit is essential in our lives.  If a home does not have an HVAC, they may have window units to keep the home cool.

As with most household appliances, maintenance is required.  What causes an air conditioner to freeze up? Lack of airflow, dust on the coils, low on refrigerant, damaged blower, dirty air filters, thermostat issues, drainage to name a few.

There can also be issues with the float switch and super cooling. Let’s take a look at the warning signs, the causes and what to do if it freezes up.


To cool a home, the coils need to have cold refrigerant. The warm air blows over the refrigerant and then the cold coil pulls the indoor heat through. This results in the air going out of the outdoor compressor unit and into the backyard.

However, if something blocks the warm air from passing over the coils, they can become too cold and freeze. When humidity is high, this is the worst time for issues with the air conditioning system.

The warm air can cause the ice to accumulate on the coils and freeze. Resulting in it forming on the copper pipes and no warm air is able to get through.

Warning Signs Your Air Conditioner Might Freeze Up

If the air supply registers in the home are warm, that might be an indicator. Open up the panel that is in the supply register and check for ice. Furthermore, if you see it, then the coils are frozen over. It is time to call a professional for assistance.

If you hear rattling sounds or irregular sounds from the blower motor inside the unit, call a professional to inspect the unit. This could be a sign that it is about to go out. The professional will tell you if it can be repaired or if you need a new system.

What causes an air conditioner to freeze up
Dirty air filter will cause an air conditioner to freeze up

What Causes an Air Conditioner to Freeze Up

Lack of airflow can cause an air conditioner to freeze up

Air conditioning units need the air to continue to flow through in order to make its escape outside. However, when it doesn’t escape, the humidity builds up and causes water to freeze on the coils. One way to prevent this is to change out the dirty air filters.

If you have pets in the home or people who smoke, this may need to be done more often. A clean air filter can help keep your air conditioning running smoothly. In fact, use a good air filter as seen here and change it at least every 3 months. You might need to change it every month if you have many people and pets in the home.

Blocked or Crushed Duct

If a duct(s) is blocked or crushed in the attic, this can cause the air to stop flowing which prohibits the coils from breathing properly.

Blower Motor

The blower motor allows the air to continue to flow through and if it stops working, the air will no longer be able to get through. Humidity will settle in and cause freezing on the coils.

Electricity issues can cause an air conditioner to freeze up

If the fan is not getting enough voltage, this can cause issues as it requires a high voltage to power it and get the air flowing to where it needs to go.

Dust on the coils

Conducting preventative maintenance can keep the dust off the coils by keeping the air filter clean. If not, the dust will create a blanket or covering on the coils and block the airflow.

Low Refrigerant can cause an air conditioner to freeze up

If there is not enough refrigerant, it can drop in pressure, expand, become too cold, and cause freezing. If you suspect this is what is going on, contact a professional to help. Refrigerant isn’t an area for the untrained to handle.

What causes an air conditioner to freeze up
Super-cooling on an air conditioning unit


The A/C differential should be between 14 and 24 degrees. If your air conditioning is cooling more than that, you risk having your A/C freeze over itself. To check the differential, use a thermometer to temp the air going into the unit, then temp the air coming out of the unit. This can be done by punching a small hole in ductwork/board to get the air temp as soon as the air goes in/out.

Broken Thermostat Can Cause the Air Conditioner to Freeze Up

This can leave the A/C in an always-running state, which will inevitably cause the unit to freeze over.

Inspecting the Float Switch

Check the float switch to see if that backed up. If the float switch is triggered,  the A/C unit will turn off. This can occur if there is a blockage in the drain.  Vacuuming with a shop vac or calling a professional can fix it. In order to maintain a float switch, use vinegar to clean it every 1-3 months.

What to Do If The Air Conditioner Freezes Up

Clear the evaporator coils

First, call a professional if you need help to clear the evaporator coils. Then, turn off the breaker and turn off the system for several hours so you can let the ice thaw. Third, once the ice has thawed, you can wipe down the coils.

Remember that the coils are dirty so if you turn the system back on without cleaning, the ice will form again quickly. Unfortunately, then mildew will form, thus not allowing the system to work properly.

Install a humistat (in warmer climates)

Warm and humid climates have issues when the humidity heats up. If it goes above 60% in the home, the following can happen:

  • Mold and mildew growth
  • Expanding of windows and doors can cause air leaks
  • Pages in books can turn yellow
  • Bacteria starts to grow
  • Overtime working of the air conditioning system, thus raising the electric bill
  • Formation of condensation will freeze the coils

Schedule preventative maintenance

Schedule a tune-up twice a year and change the air filters as often as needed. The air filter may need to be changed more often depending on dust and other particles in the home. These things can help you get to the predicted lifespan of 15-20 years for an air conditioning system.


Air conditioning is very important to keep working in the home.  Scheduling maintenance, and keeping an eye on the unit can save you money and aggravation. The above tips help with understanding what causes an air conditioner unit to freeze up.

If you have questions about this or need our assistance, please drop us a line below! We at Atkinson Inspection Services are here to help!