Dehumidifier shows E4 and will not run the compressor

Safety: Unplug the unit. Do not attempt to open the sealed refrigeration system yourself—refrigerant work must be done by a licensed technician.

Basic user-level checks:

• Clean air filters and grilles: Remove and wash the air filter with mild soap and water. Vacuum dust from the intake and exhaust grilles. Restricted airflow can cause pressure faults.
• Check room temperature: Ensure the room is within the operating range. Very low ambient temperatures can trigger protection codes.
• Inspect the fan operation: Plug the unit back in and run in fan-only or dehumidify mode. Confirm the fan runs smoothly and at normal speed. If the fan is not running, see the separate fan motor fault entry.
• Allow cool-down: If the unit has been running continuously, leave it unplugged for 30–60 minutes to allow the compressor to cool, then retry.

Advanced checks (technician recommended):

• Inspect the pressure switch / sensor wiring for damage or disconnection.
• Measure system pressures and check for refrigerant leaks.
• Test compressor current draw and thermal overload.

If E4 persists after cleaning and ensuring proper airflow, contact a professional. The likely repair involves replacing the pressure switch/sensor, repairing leaks, and recharging refrigerant, or replacing the compressor if it is failing.