Dehumidifier displays P4 and stops operation unexpectedly.

Safety: Unplug the unit before accessing internal components.

• Reset: Disconnect power for 10 minutes and restart. If P4 returns, continue.
• Locate defrost sensor: On many TCL models, the defrost sensor is the same as or located near the evaporator temperature sensor, clipped to the coil.
• Inspect wiring and clip: Ensure the sensor is firmly attached to the coil and the wires are not damaged or pulled loose.
• Test sensor: Measure resistance at room temperature and compare to TCL’s NTC chart. Replace if open, shorted, or far out of range.
• Board diagnosis: If a known-good sensor still results in P4, the defrost control circuit on the main PCB is likely defective and the board should be replaced.