Safety first: Turn OFF power at the breaker before inspecting the outdoor unit.

Step 1 – Inspect outdoor coil and fan: Ensure the condenser coil is clean and the outdoor fan is running properly (see E3 procedure). Correct any airflow issues.
Step 2 – Check ambient conditions: In very high outdoor temperatures, reduce the thermostat setpoint gradually and ensure the unit is not operating with doors/windows open, which can overload the system.
Step 3 – Sensor check: A technician should verify the compressor discharge temperature sensor (usually clipped to the discharge line) is firmly attached and not damaged. Replace if its resistance is out of TCL specifications.
Step 4 – Refrigerant diagnosis: If E4 repeats, a professional should check for low charge, restrictions, or compressor mechanical issues. Running the unit in this condition can permanently damage the compressor.

Warning: Do not bypass temperature sensors or run the unit continuously with E4 errors; this can cause compressor failure.

Unit displays E4 and stops heating or cooling; may restart after some time

Possible Causes