Freezers are convenient appliances that help to store large amounts of food in the home. There are basically two types--chest freezers and upright freezers. Chest freezers have the door on the top of the unit, while uprights resemble compact refrigerators. In the past, freezers had to be defrosted manually. This was a time-consuming process. You had to remove all the food, turn off the freezer, open the door and then let all the ice melt. But now many freezers are frost free or self defrosting.
The Parts of a Self-Defrost System
There are three parts to an automatic self-defrosting freezer: the timer, heating coil and temperature sensor or thermostat. The timer has two variations. One works like a clock and runs continuously for 24 hours a day. The other runs at set intervals such as every 6 to 8 hours. The heating coil is intertwined with the freezing coil in some models. In other models, there is a defrost heater that lies directly below the freezing coils. Both the heating coil and defrost heater serve the same purpose--to melt the ice. Both heating elements are very similar to the burners found on electric ranges. The thermostat senses the temperature inside the freezer and determines when it is time to turn off the heating element and end the defrosting process.
How Self-Frosting Works
There is always moisture or water vapor in the freezer. This usually happens when you open the freezer door. As the cold air blows, this moisture turns to ice and frost which build up. Self-defrosting freezers are one way to get rid of the ice. The defrosting process starts when the timer turns off the cooling system and turns on the defrost heater. This occurs every 6 or 8 hours. When the heating coil is on, it warms up and starts to melt all the ice in the freezer. Because the heating coil or heater is so close to the cooling coil, it take only about 20 to 30 minutes to completely melt all the ice build-up. As the ice melts the temperature in the freezer rises. The thermostat senses that the air in the freezer is now above the 32 degrees Fahrenheit freezing mark. The thermostat then turns off the heating coil and the cooling system turns on again. In other models, it is the timer that determines when the heating element is turned off and not the thermostat. All the melted water drips into a trough that is attached to a tube that drains out all the water to a pan at the bottom of the freezer where it evaporates. Once the cooling system is back on, it freezes the moisture and creates ice. In 6 to 8 hours, the defrosting cycle starts again.