AUTOMATIC DEFROSTING BASIC AND TUTORIALS


Automatic defrost
Frost-free refrigerators and freezers call for some means of timing the defrost cycle. As the frost accumulates in the freezer and refrigerator sections, it must be removed.

It is easily removed if done often enough to avoid a buildup. The defrost timer is used to control how often the defrost cycle takes place (see Fig. 17-6).


Contacts 1 and 3 are used for the defrost-motor coils. Contacts 2 and 4 are used to make contact with the proper circuit components to provide energy to the defrost heater or compressor (see Fig. 17-7).


The termination thermostat shown in the circuit is located near or on the evaporator to sense its temperature and indicate that the defrost cycle is complete and has done its job of removing the frost from the evaporator. The defrost timer can be located in any number of places.

Note the addition of other features, such as a drip catcher heater, mullion heater, and door heater. These heaters serve different purposes.

The drip catcher heater allows the water that forms during defrost to drain out of the freezer unit to a pan underneath to be evaporated by the heat of the compressor nearby. The mullion heater and door heater are used to prevent a frost buildup on and around the doors of the freezer and refrigerator compartments when the outside air is very humid.

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