Meridian Boise Appliance Repair - Refrigerator Defrost Operation

I am the owner of Western Boise Appliance Repair with two location in Boise and one in Meridian idaho.  I'd like to share some thoughts or actually, to give some advice and enlightenment on the defrost operation on most side by side, bottom-mount, top-mount refrigerators.  Many brands of refrigerators operate on the same principles whether they are GE, Whirlpool, Kenmore, Maytag, Sears, or Frigidaire. Here we go, to put in a nutshell, the refrigerator evaporator, which in most cases is located in the Freezer, absorbs heat from the inside of the Freezer.  Think of the refrigerant as tiny sponges that are flowing through the evaporator that will absorb the heat.  Thinking in layman's terms like this will make understanding this a lot easier.  Ok, the evaporator coils absorb the heat and has it does, it causes condensation on the evaporator coils.  This condensation quickly freezes on the refrigerator coils and turns into frost.  The more the freezer and refrigerator doors are opened and closed, the more air and moisture enters the refrigerator/freezer.  The more moisture, the more frost.  If there wasn't a way to get rid of that frost, your freezer evaporator area would turn into one big blog of frost or ice.  Now we'll talk about the defrost operation.
Engineers had to devise a way to defrost the evaporator coils and still allow cooling in the refrigerator.  Most early refrigerator models use a timer, heater, bi-metal combination.  I'll talk about each one of these separate:
Heater:  On most models, GE, Whirlpool, Kenmore, Maytag, a heater bar is positioned on the bottom of the evaporator.  The compressor turns off and AC current flows through the heater to make it glow red hot and to radiate heat.  Since heat rises, it radiates upward to melt all the frost off the refrigerator appliance's evaporator coils.  Well, this heat can't go on forever otherwise we would cause the refrigerator/freezer to warm.  So, enter the appliance's timer mechanism.
Timer:  Approximately every 8 hours, the timer will switch off AC Power from the compressor and switch it to the heater.  The duration is controlled by the timer, usually 20-30 minutes.  When the 20-30 minute defrost has been completed, the timer switches AC Power from the heater, back to the appliance's compressor , evaporator and condenser fan motors.
Bi-Metal:  The refrigerator's bimetal acts as a "safety" to guarantee the evaporator does not get too warm.  It is usually located at the top of the evaporator.  To be plain, it is actually a switch/thermostat wired in series with the defrost heater and it is engineered to open and close at a predetermined temperature.  It closes when it is cold and it opens the circuit when it's warm, usually from 35-55 degrees Fahrenheit.
Hope this helps some of your appliance repair questions and you can always visit us for more topics and articles.