To repair a frozen dehumidifier, raise the room temperature above 65 degrees Fahrenheit, clean the filter, or vacuum the condenser coils. Moving the frozen dehumidifier away from the wall to allow free-flowing air into the unit can also fix the appliance.
A low room temperature is the most common cause for a frozen dehumidifier, and it can be fixed by maintaining a higher room temperature or using a basement dehumidifier, which is designed to operate in cool conditions. Elevating the dehumidifier can also prevent freezing by allowing the unit access to slightly warmer air. Cleaning the filter can repair a frozen dehumidifier by removing dirt and dust, which cause airflow blockage. Most filters can be vacuumed, but foam filters need to be cleaned with running water.
If dirty condenser coils are the cause of a frozen dehumidifier, unplug the appliance, and remove the screws holding the cover. Check to see if the coils are completely frozen or partly iced over. For completely frozen coils, allow time for ice to melt and water to evaporate, then use a brush attachment to vacuum dust from the coils. If the coils are not clean after vacuuming, cover the dehumidifier's electrical parts with plastic sheeting, and then spray water on the coils to remove dirt. Allow the dehumidifier to drain and dry completely before reassembling and plugging it in.
Partially frozen coils indicate a low level of refrigerant or a failed compressor, and both problems require a dehumidifier replacement or professional repairman.