The Clean Filter LED turns on after 250 to 500 hours of use.   The time depends on the model of the air conditioner or dehumidifier.   The Clean Filter LED is only a reminder to clean the filter and not an actual sensor.   To turn off the Clean Filter LED hold down the Filter button for 5 to 10 seconds to reset the timer.

On AC models that do not have a Clean Filter button hold down the Fan or Fan Speed button to clear the light.