Turn it off first
Before troubleshooting, switch the system to "OFF" (or set it to "FAN ONLY" to help it thaw faster). Running a frozen system can slug liquid refrigerant back to the compressor — the most expensive part to replace. Let it thaw for 1–3 hours.
The most common causes
1. Dirty air filter or blocked airflow
This is the #1 cause. When airflow over the indoor coil drops, the coil gets too cold and condensation freezes. Check your filter — if you can’t see light through it, replace it. Also make sure supply and return vents aren’t blocked by furniture or closed.
2. Low refrigerant (a leak)
Low refrigerant drops the coil pressure and temperature until it freezes. Refrigerant doesn’t get "used up" — if you’re low, you have a leak that needs to be found and repaired, not just topped off.
3. Dirty evaporator coil
Over years, dust builds up on the indoor coil and insulates it, leading to freezing. This is cleaned during a professional tune-up.
4. Failing blower fan
If the indoor blower motor is weak or failing, it can’t move enough air across the coil, causing ice to form.
What you can safely do: Replace the filter, open all vents, and let the unit thaw. If it freezes again after that, it’s time for a professional — the remaining causes need tools and refrigerant certification.
When to call a technician
Call us if the system refreezes after a filter change and thaw, if you see oily residue near the lines (a refrigerant leak sign), or if airflow is weak from every vent. We’ll find the root cause — airflow, refrigerant, or the blower — and fix it before it turns into a compressor failure on a 105° afternoon.
Frequently Asked Questions
It’s safer to simply turn the system off (or run the fan only) and let it thaw naturally. Avoid chipping at the ice, which can puncture the coil.
It’s not dangerous, but you should stop running it immediately to protect the compressor. If it refreezes after a filter change and thaw, schedule service promptly.
Cooler nighttime temperatures plus an already-marginal airflow or refrigerant problem can tip the coil into freezing. It points to an underlying issue worth diagnosing.
No. Refrigerant is in a sealed loop, so being low means there’s a leak. It needs to be located and repaired, then recharged to the correct level.