It sounds strange, but air conditioners can freeze even in the middle of a Southern California heat wave. If you see ice on the copper lines near the outdoor unit, frost on the indoor coil or water around your furnace or air handler, your AC is freezing up. Here is why it happens and what to do.
What to do right away
- Turn the thermostat to Off so the compressor stops running. Running a frozen system can damage the compressor.
- Set the fan to On to move warm air over the coil and speed up melting.
- Check and replace the air filter.
- Watch for water. Melting ice can overflow the drain pan. Put towels down and check the condensate drain.
- Wait until the ice is completely gone — often a few hours — before turning cooling back on.
Do not chip or scrape ice off the coil. The fins and tubing are easy to damage.
Common causes of a frozen AC
Restricted airflow
The indoor coil needs a steady stream of warm air passing over it. When airflow drops, the coil gets too cold and moisture freezes on it. Common causes are a dirty filter, closed or blocked vents, a dirty coil, a failing blower motor or collapsed ductwork.
Low refrigerant
A refrigerant leak lowers the pressure in the system, which lowers the coil temperature below freezing. If your AC freezes repeatedly even with a clean filter, low refrigerant is a likely cause. It needs a technician to find and repair the leak.
Running the AC when it is cool outside
Air conditioners are designed to run when outdoor temperatures are warm. Running cooling on a cool night — common in foothill areas like La Crescenta and Tujunga — can cause the coil to ice up.
Thermostat set very low
Setting the thermostat far below a comfortable temperature does not cool the house faster. It only makes the system run longer, which can contribute to freezing when airflow is already marginal.
Drain problems
A clogged condensate drain does not freeze the coil by itself, but it can cause water damage when the ice melts. Many systems have a safety switch that shuts the AC off if the drain backs up.
How to prevent your AC from freezing
- Change the filter regularly — every 1–3 months during cooling season
- Keep supply vents and return grilles open and clear
- Schedule a spring AC tune-up: coil cleaning, refrigerant check, airflow and drain inspection
- Avoid very low thermostat settings; 74–78°F is a good range for most homes
When to call for service
If your AC freezes more than once, if you hear hissing or bubbling, or if the system blows warm air after the ice melts, call for AC repair. Freezing is a symptom — the fix is finding the cause. Related: AC blowing warm air? 8 common causes.
Schedule AC repair
Orion HVAC serves La Crescenta, Glendale, Burbank, La Cañada Flintridge, Tujunga, Santa Clarita and the San Fernando Valley. Call (323) 736-3737 or book online. You get the price before any work begins, and every repair is backed by our parts and labor guarantee.
