There are four types of defrosting mechanisms: (1) Automatic, (2) Semi-Automatic, (3) Cyclical and (4) Frost-free. Semi-automatic refrigerators are defrosted by manually pushing a button to begin the defrost cycle. Once the button is pushed, the defrosting is done automatically. Automatic mechanisms defrost the fresh-food compartment automatically, but the freezer still has to be defrosted manually.In cyclical defrosting, the defrosting function is activated every 8 hours by a timer. The defrosting cycle lasts 20 minutes and the frost evaporates automatically. Frost-free refrigerators have an in-built thermostat, heater and a timer that activates the defrost cycle every 2 hours.