This one needs a licensed pro
Likely cause: low refrigerant or a dirty coil
Ice that keeps coming back with a clean filter and open vents usually means low refrigerant or a dirty indoor coil. Thaw it, then call an HVAC technician.
Why this happens
Trane, Lennox and Carrier all list low refrigerant and a dirty evaporator coil among the causes of a frozen AC, after airflow problems are ruled out. Low refrigerant means a leak somewhere in the system. The EPA says "only Section 608 certified technicians can purchase refrigerants intended for use with stationary refrigeration and air-conditioning equipment," and its rules prohibit venting refrigerant while servicing a system. Lennox says homeowners should not handle refrigerant.
What to do right now
- Set the thermostat from Cool to Off, then set the fan to On to thaw the ice. Carrier and Lennox both suggest this.
- Don't chip at the ice and don't use a hair dryer or space heater. Carrier and Trane both warn against it.
- Put towels around the indoor unit and watch the drain pan as the ice melts.
- Leave the AC off until the technician comes. Carrier warns that a frozen AC will not fix itself and running it risks the compressor.
- Don't buy a refrigerant recharge kit or open the unit.
What to tell the HVAC technician
- How many times it has frozen and how long it ran between freezes.
- That you replaced the filter and opened every vent and it still refroze.
- Any hissing sound or oily residue near the lines or units.
- The brand, model and serial from the outdoor unit's data plate.
Build the full list: what to tell the HVAC technician.
Start this troubleshooter over
Vent, Valve & Volt is published by the team behind FourHome. Browse all FourHome replacement faucet and shower parts on the FourHome Amazon store.