Freezer Basics - How They Work

If you have ever had an old refrigerator or sent a child off to college with a small dorm refrigerator, you know all about the frost that forms around the coils that cool the freezer. If you let it build up long enough, the frost can get so thick that eventually there is no room to put anything in the freezer.

This frost forms when water vapor hits the cold coils and condenses, turning to liquid. This is similar to how water beads on a cold beverage glass on a hot summer day. The same thing happens on the ice-cold freezer coils, except that when the water condenses onto the coils it immediately freezes.

Automatic defrost or frost-free freezers have three basic parts:

  • A timer (intermittent - advances every 6-to-8 hours or continual- runs 24 hours like a clock)
  • A heating coil
  • A temperature sensor

Every six hours or so, the timer turns on the heating coil. The heating coil is wrapped among the freezer coils. The heater melts the ice off the coils. When all of the ice is gone, the temperature sensor senses the temperature rising above 32 degrees F (0 degrees C) and turns off the heater.

Heating the coils every six hours takes energy, and it also cycles the food in the freezer through temperature changes. Most large chest freezers therefore require manual defrosting instead -- the food lasts longer and the freezer uses less power.


Understanding freezer cooling systems is easier if you think of their action as "removing heat from the air in the freezer" rather than "cooling the air in the freezer." All residential freezers work on the same principle for cooling. They all have:

  • A compressor - motor or engine of the cooling system
  • A condenser - series of tubes or fins that act like a radiator
  • A metering device (capillary tube) - controls the pressure and flow of the refrigerant as it enters the evaporator.
  • An evaporator - functions as a heat absorber when the refrigerant changes state from liquid to gas

Temperature control

Freezers have a thermostat to maintain the proper temperature. When the freezer reaches the set temperature, the thermostat interrupts the electricity flow to the compressor, which stops cooling.

Door seals and hinges

Freezer doors have a a rubber-like gasket or seal attached to the door. The seal is lined with a magnet that runs its length and width. The magnet helps to hold the door closed and creates a tight seal. The screws that hold the seal to the door also hold the door liner in and help to "square" the door.

The hinges allow the door to swing open. Some hinges also assist the door in closing. For the door to close properly, the hinges must be correctly adjusted.

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