Lennox Air Conditioner Error Code E422

E422 means the compressor top cap thermal switch has detected that the compressor temperature has exceeded its safe operating limit. The outdoor control board receives this signal through the TP terminals and shuts the system down to protect the compressor from damage. The fault can result from genuine overheating or from a wiring issue at the TP terminals on the control board.

No. The E422 fault indicates the system has already shut down to protect the compressor from heat damage. Attempting to bypass or ignore this fault and force the system to run risks permanent compressor failure, which is one of the most expensive repairs on an air conditioner. The system should remain off until the root cause is diagnosed and corrected.

Repair costs vary widely depending on the cause. A simple wiring fix or condenser coil cleaning may cost between $75 and $200 in labor. Replacing the top cap thermal switch typically runs $100 to $300 including parts and labor. If the compressor itself has failed, replacement costs can range from $1,200 to $2,800 or more depending on the unit size and labor rates in your area.

A homeowner can safely inspect and reseat the wiring connections at the outdoor control board's TP terminals, which is the first recommended diagnostic step. However, diagnosing the underlying cause of actual compressor overheating, including checking refrigerant charge, testing the thermal switch, or evaluating the compressor, requires specialized tools and EPA certification for refrigerant handling. A licensed HVAC technician should perform those steps.

A power reset may clear the fault temporarily if the compressor has cooled down, but the code will return if the underlying cause has not been addressed. If the fault reappears quickly after a reset, the system has a genuine thermal or wiring problem that needs to be repaired. Repeated resets without fixing the root cause can shorten the compressor's service life.