A frost-free freezer uses a timer, heating coil and temperature sensor to keep frost from forming around the cooling coils inside the unit. Frost forms when water vapor runs into the coils. However, a frost-free freezer melts that ice with a heating coil to keep frost from aggregating.
The timer in the unit turns on the heating coil about every six hours. The heating coil snakes through the freezer coils and melts the ice off. The temperature sensor turns the heating coil off when it notices the temperature going higher than 32 degrees Fahrenheit. This increases power use but keeps the freezer from gradually filling up with frost.