You can fix this
Likely cause: blocked vents or return grilles
Closed or blocked vents cut the airflow the coil needs. Open them up, thaw the ice, and it should stop.
Why this happens
Trane lists blocked return vents and Lennox lists blocked ducts or vents among the causes of a frozen AC. When less air moves through the house, less warm air crosses the indoor coil, and it can drop below freezing. Return grilles matter most, since they feed air back to the system.
How to fix it
- Set the thermostat from Cool to Off, then set the fan to On to start the thaw.
- Open every supply vent and move furniture, rugs and curtains off vents and return grilles.
- Don't chip at the ice or use a heat source on it. Put towels down and watch the drain pan.
- Wait until the ice is completely gone, then set the thermostat back to Cool.
- Leave vents open in unused rooms too. Closing them can work against the system.
When to stop. If it freezes again with every vent open and a clean filter, stop running it and call an HVAC technician.
If this does not fix it, tell the HVAC technician
- Which vents or returns were closed or blocked.
- Whether it refroze once they were open.
- Whether the filter was clean.
Build the full list: what to tell the HVAC technician.
Start this troubleshooter over
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