You can fix this
Likely cause: a frozen coil
Ice on the lines or the indoor coil blocks the heat exchange, so the air comes out warm. Turn the cooling off and let it thaw.
Why this happens
Trane lists a frozen evaporator coil among the causes of an AC that won't blow cold air. Ice usually forms when not enough warm air moves across the coil, often from a dirty filter or blocked vents. Carrier warns that a frozen air conditioner will not fix itself, and running it frozen risks the compressor.
How to fix it
- Set the thermostat from Cool to Off, then set the fan to On so the blower moves air over the ice. Carrier and Lennox both suggest this to speed the thaw.
- Don't chip at the ice and don't use a hair dryer or space heater. Trane says chipping can damage the coil.
- Put towels around the indoor unit. A lot of water comes off as the ice melts, so watch the drain pan and drain line.
- While it thaws, replace the filter if it is dirty and open any closed supply vents and return grilles.
- Carrier says light frost may thaw in about 1 to 3 hours and heavy ice can take 4 to 8 hours or longer. Wait until it is fully clear before switching back to Cool.
When to stop. If it freezes again after a full thaw with a clean filter and open vents, stop running it and call an HVAC technician. Repeat freezing points to low refrigerant or a dirty coil.
If this does not fix it, tell the HVAC technician
- Where you saw the ice and how thick it was.
- Whether the filter was dirty and whether any vents were closed.
- Whether it froze again after thawing with a clean filter.
Build the full list: what to tell the HVAC technician.
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