Indoor unit stops and displays E4; often occurs in heating mode on heat pump models, sometimes after long operation.

Safety first: Turn OFF power at the breaker before touching the outdoor unit. The compressor and discharge line can be extremely hot.

• Step 1 – Inspect and clean outdoor coil: Remove debris, leaves, and dust from the outdoor coil. Use a soft brush or low‑pressure water. Ensure at least 24 inches of clearance around the unit.
• Step 2 – Check outdoor fan: Restore power and run the unit in HEAT (for heat pump models). Confirm the outdoor fan starts with the compressor and runs continuously. If it stops while the compressor runs, the fan motor or control board may be faulty.
• Step 3 – Verify ambient conditions: Extremely high outdoor temperatures or blocked sunshades can cause high discharge temperature. Improve shading and airflow if possible.
• Step 4 – If E4 persists: The discharge temperature sensor may be out of range, or the system may be undercharged/overcharged. A technician should measure discharge temperature, check sensor resistance, and verify refrigerant charge.