An AC freezing up — visible ice on the large copper line at your outdoor unit, or frost on the indoor evaporator coil — is the system telling you airflow or refrigerant pressure is wrong. Running the AC like this damages the compressor. Here's what to do right now and what's actually causing it.
Most Likely Causes
1. Dirty air filter (most common)
A clogged filter restricts airflow across the evaporator coil. Less airflow means the coil temperature drops below freezing, condensation freezes on the coil, and the freeze grows backward to the line set. Fix the filter, thaw the system, and 80% of freeze-ups are over.
2. Low refrigerant
Less refrigerant means lower coil pressure, which means a colder coil, which freezes condensation. If you fix airflow and it freezes again within a day, you have a leak.
3. Dirty evaporator coil
Same problem as a dirty filter — restricted airflow across the coil. A coil that hasn't been cleaned in 5 years can be 30% blocked by dust and biological film.
4. Failing blower motor
If the motor is running slow (failing capacitor, worn bearings), airflow drops even with a clean filter and clean coil.
5. Closed or blocked supply registers
Closing too many vents to 'redirect' air actually starves the system of return airflow. Keep at least 80% of your supply registers fully open.
6. Outdoor temperature too low
Most central AC systems aren't designed to run below 60°F outdoors. If you're trying to use AC in 50° weather, expect freezing. Switch to fan-only or open windows.
Try These Steps Before You Call
- Turn the AC OFF immediately. Set the thermostat to 'off' on cooling — but switch the fan to 'on'.
- Wait 2–3 hours for the coil to fully thaw. (Yes, really — partial thaw and restart will refreeze instantly.)
- Check and replace the air filter.
- Check that all supply registers are open.
- After full thaw, switch back to 'cool' and watch for cold air.
- If it freezes again within 24 hours, call us — you have a deeper issue (refrigerant leak, dirty coil, motor problem).
Still not working?
Don't run a frozen AC — you'll burn out the compressor. Call (214) 466-6465 if it freezes again after thawing and a filter change.
Call (214) 466-6465