Abstract: The invention relates to defroster control apparatus for the evaporator of a refrigerator. A frost sensor for measuring temperature is mounted a predetermined distance from a surface of the evaporator which corresponds to the permissible thickness of frost layer. Control apparatus including a comparator circuit initiates defrosting when the frost sensor temperature falls below a reference temperature. In this construction the frost layer grows in the direction of the frost sensor which is swept by the surrounding air. During each operating cycle the frost sensor initially measures a temperature approximating to the surrounding temperature. As the frost progressively increases, this temperature falls because the air circulation in the vicinity of the frost sensor is progressively more influenced as the thickness of the frost layer increases. In the extreme case, the frost sensor can come into contact with the frost layer.

Abstract: The invention relates to a refrigeration assembly and particularly to defrosting apparatus therefor. The assembly includes a bellows operated thermostatic motor switch responsive to evaporator temperatures for operating the compressor motor. After a predetermined number of operating cycles of the compressor the defrost apparatus is actuated. There is a linkage between the bellows and the motor switch with a main spring acting thereon to oppose the bellows and a differential spring acting thereon to assist the bellows. The differential spring is made inoperative by the defrosting unit during the defrost setting. The main spring and the differential spring are calibrated so that when both springs are effective the motor switch is actuated at a predetermined evaporator temperature. When only the main spring is effective during the defrost setting the motor switch is actuatable at an evaporator temperature higher than the above referred to temperature.