Disconnect power to the dehumidifier.
Remove the screws holding the front panel in place and lift off the panel.
Disconnect the sensor assembly from the main control panel and remove the screw holding the humidity sensor in place.
Use a cloth dampened with rubbing alcohol to clean the sensor and let the sensor air-dry.
Replace the humidity sensor and screw into place, then return the main panel and fasten the panel into place.
Restart the dehumidifier and monitor its performance. If the sensor does not seem to be working better, contact the dehumidifier manufacturer for assistance.