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Likely cause: a clogged air filter
A clogged filter is the first cause Trane, Lennox and Carrier name for a frozen AC. Thaw the ice, replace the filter, and it usually stops.
Why this happens
When the filter clogs, too little warm air crosses the indoor coil, so the coil gets cold enough for the moisture on it to freeze. Trane lists a dirty filter first for a frozen evaporator coil, and Carrier puts restricted airflow first. Trane's air handler page recommends replacing the filter every 30 to 90 days.
How to fix it
- Set the thermostat from Cool to Off, then set the fan to On to start the thaw.
- Replace the filter with the same size, arrow pointing toward the furnace or air handler.
- 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. Carrier says light frost may take 1 to 3 hours and heavy ice 4 to 8 hours or longer.
- Set the thermostat back to Cool and check the lines again the next day.
When to stop. If it freezes again with a clean filter and open vents, stop running it and call an HVAC technician.
If this does not fix it, tell the HVAC technician
- When the filter was last changed and how dirty it was.
- Whether it refroze after the new filter.
- How long the thaw took.
Build the full list: what to tell the HVAC technician.
Start this troubleshooter over
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