Safety first: Unplug the unit and allow any ice on the coils to melt before working inside.

Steps to resolve P4:

Allow defrost: If the unit has visible ice on the evaporator coil, leave it unplugged with the front grille removed for 1–2 hours to fully defrost. Then restart and see if P4 clears.
Access the evaporator: Remove the front or side cover (consult your Whynter manual). Locate the small sensor (thermistor) clipped or taped to the evaporator coil tubing.
Check sensor placement: Ensure the thermistor is firmly attached to the coil and not hanging loose. Re-clip or re-tape it if necessary using aluminum tape or the original clip.
Inspect wiring: Follow the thermistor wires back to the control board. Look for cuts, pinched sections, or loose connectors. Reseat the connector on the board.
Test operation: Reassemble the unit, plug it in, and run it. If P4 returns immediately, the defrost sensor or control board likely needs replacement.

Warning: Do not bend or puncture the refrigerant tubing while working around the evaporator coil.

Dehumidifier shows P4 and shuts down or will not start

Possible Causes