Vent, Valve & Volt
Ice on your AC lines or coil

You can fix this

Likely cause: running the AC in cool weather

Lennox warns that running the AC when it's below about 60F outside can freeze the coil. Thaw it and give the AC a rest until it warms up.

Why this happens

Lennox lists running the AC below 60F among the main causes of a frozen unit. On cool days, the coil runs colder than it's designed to, and moisture freezes on it instead of draining away. Carrier notes a frozen AC won't fix itself, so it still needs a full thaw.

How to fix it

  1. Set the thermostat from Cool to Off, then set the fan to On to speed the thaw.
  2. Don't chip at the ice or use a heat source on it.
  3. Put towels around the indoor unit and watch the drain pan as it melts.
  4. Carrier says light frost may thaw in about 1 to 3 hours and heavy ice in 4 to 8 hours or longer. Wait until it's fully clear.
  5. On cool days, open windows or run the fan instead of the AC.

When to stop. If it freezes again in warm weather, the cause is something else. Work back through the questions or call an HVAC technician.

If this does not fix it, tell the HVAC technician

  • The outdoor temperature when it froze.
  • Whether it has frozen in warm weather too.
  • Whether the filter was clean.

Build the full list: what to tell the HVAC technician.

Start this troubleshooter over

References (every fact above comes from one of these pages)
  1. Lennox: AC unit freezing up
  2. Carrier: Will a frozen AC fix itself?

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