Why Is My AC Freezing Up?

Ice on your air conditioner in the middle of a Northern Virginia summer feels backwards, but it is a common problem with a few clear causes. Almost every frozen AC comes down to restricted airflow or low refrigerant. The first thing to do is turn the system off, then work through the checks below.

First, turn it off

Running a frozen system is the one thing that can turn a cheap fix into an expensive one. Ice on the coil forces the compressor to work against a wall, and the compressor is the costliest part of the whole system. Switch the AC off at the thermostat (you can leave the fan on Auto), and let it thaw before you do anything else.

1. A dirty air filter

This is the number one cause. A clogged filter starves the coil of the warm air it needs to keep from freezing. If you cannot remember the last time you changed it, that is very likely the problem. Replace it and you have solved most freeze-ups.

2. Blocked or closed vents

Closing too many supply vents, or blocking returns with furniture or rugs, chokes airflow the same way a dirty filter does. Open your vents and clear anything covering the returns.

3. A dirty evaporator coil

Over time the indoor coil collects dust that insulates it and drops its temperature until it freezes. This one is a professional cleaning, since the coil is delicate and easy to damage.

4. Low refrigerant from a leak

Low refrigerant drops the pressure and temperature in the coil below freezing. Refrigerant does not get used up in normal operation, so low levels almost always mean a leak. This is not a DIY fix: handling refrigerant requires EPA certification, and topping it off without repairing the leak just wastes money.

5. Fan or thermostat issues

A failing blower motor, a bad capacitor, or running the AC on an unusually cool night can all let the coil freeze. If the filter is clean and vents are open but it keeps icing up, the cause is one a technician should diagnose.

What to do right now

Turn the system off and let the ice melt completely, which can take a few hours. Replace the filter, open all the vents, and clear the area around both the indoor and outdoor units. Then turn it back on. If it cools normally, you are likely back in business. If it freezes again, stop and call, because the cause is deeper. For related airflow issues, see our guide to why an AC runs but will not cool.

Elite Air is a Class B licensed Virginia HVAC contractor (DPOR 2705159611) and an Independent Trane Comfort Specialist serving Northern Virginia since 2012, with 24/7 emergency service when your AC quits in the heat. If your system keeps freezing, we will find out why and fix it right.