Why Is My AC Freezing Up? Causes & What to Do

Finding ice on your air conditioner during summer feels backwards — but a frozen AC is one of the more common calls we get. Here's why it happens and what you should (and shouldn't) do.

First: turn it off

Running a frozen AC can damage the compressor — an expensive repair. Switch the system to OFF, then set the fan to ON to help the ice melt faster. Give it a few hours to fully thaw before troubleshooting.

Common causes of a frozen AC

• Restricted airflow. A dirty filter, closed or blocked vents, or a dirty blower starves the coil of warm air, so condensation on it freezes. This is the #1 cause — and the easiest to prevent.
• Low refrigerant. A leak drops the pressure in the system, causing the coil to get cold enough to ice over. This needs a licensed tech.
• A dirty evaporator coil. Dust insulates the coil and disrupts heat exchange, leading to freezing.
• Running the AC when it's too cool out. Running it on a 60°F night can cause freezing — most systems aren't designed to cool when it's already cold outside.

What you can do yourself

After the ice melts: replace the air filter, open all the supply and return vents, and make sure furniture or rugs aren't blocking airflow. Then restart and see if it cools normally.

When to call us

If your AC freezes again after a thaw and a new filter, you likely have low refrigerant or a coil issue that needs a professional. Lumen offers fast AC repair throughout the Philadelphia area — call (267) 252-2969 and we'll get to the bottom of it.