Even during a scorching Kansas summer, when temperatures outside soar, ice can build up on or inside your air conditioner. This can lead to big problems, so it’s important to know why ice can form on an AC unit and how to prevent your air conditioner from freezing up.

First things first: If you have ice on your air conditioner, shut the unit off now to allow it to defrost while you read on to determine whether you need to call a professional for service.

Why does an air conditioner freeze up?

If your air conditioner freezes up, it’s either because something is preventing heat from transferring from your house to the Freon, or something is causing the evaporator coils to get too cold.

Air conditioners work by transferring heat through a refrigerant called Freon. The evaporator coil expands the Freon, which causes the coil to cool quickly. Air is blown over the cold coils and distributed through your home’s duct work to cool the air in your house. The refrigerant inside the coils absorb the heat from the air, then moves outside your home to the compressor. The compressor causes the Freon to release the heat from your home into the outside air, and they cycle starts again.

What causes ice on the outside of an air conditioning unit?

Cause: Low refrigerant level
If your refrigerant is low, you have a leak. This causes the Freon to expand too much in the air conditioner’s evaporator coil, lowering the temperature below freezing and causing ice to form.
Solution: Have a qualified HVAC technician repair the leak and recharge the coolant.
Prevention: Have your air conditioner inspected and serviced every spring to catch potential problems and make sure it has the right amount of Freon.

Cause: Dirty evaporator coil
A dirty evaporator coil can cause ice to form on your air conditioner because it restricts airflow through the unit. A dirty coil can also make the AC unit use more electricity while producing less cool air, and cause significant damage to the compressor.
Solution: To prevent your cooling system from breaking down completely, shut the unit off until the coil is cleaned or replaced by a professional.
Prevention: Clean the evaporator coil regularly.

Cause: Restricted Airflow through the AC unit
In order to function properly, air conditioners rely on air flowing through the system. Too little airflow reduces the temperature, causing the AC unit to freeze up. Airflow can be restricted by dirty air filters, closed vents, or by clogs or leaks in the ductwork.
Solution: Depending on what’s restricting the airflow, you may need to change your air filter, clean your ductwork or repair your air ducts.
Prevention: Change the air filter once a month during heavy-use times like summer, and consider having your ductwork sealed.

Cause: Outside temperature is too cold
Air conditioners weren’t designed to be used when the outdoor temperature is below 62 degrees Farenheit. This isn’t usually an issue here in Wichita, except during the late spring and early fall, when temperatures can get into the 70s and 80s during the day but drop down into the 50s overnight.
Solution: Turn off the AC unit to allow it to thaw.
Prevention: Turn off the air conditioner at night when the temperature is predicted to be in the low 60s or lower.

Cause: Mechanical failure
Broken valves, a damaged blower fan or fan motor, kinked refrigerant lines, or a blocked drain can all cause your central cooling system to freeze up.
Solution: Have a licensed HVAC professional inspect and repair the unit.
Prevention: Regular maintenance of your heating and cooling systems, generally in spring and fall, will ensure all parts are working properly.

How do I know if there’s ice inside my air conditioner?

Ice inside your AC unit can’t be seen as easily, but it can cause serious damage so it requires service immediately. In the humid climate here in the Midwest, it’s common for air conditioners to drip water. But, if a lot of water is dripping inside the unit, that’s a sign of trouble. A full drip pan can indicate melted ice inside the AC system. Another red flag is the sound of ice chunks falling, like when your refrigerator defrosts. If you notice either of these signs, shut off the unit and call an air conditioning technician right away.

For all these problems, prevention really is the best cure. Having your air conditioner inspected and tuned up each year will keep the system ice-free and running efficiently for years to come.