The crankcase heater is a resistive heater that either mounts around the bottom of the body, or is an insertion type that slips into a well in the body, or a bar type that fastens to the bottom of the crankcase. It is the function of this component to energize on the compressor off cycle and transmit heat into the crankcase. The reason for this is to boil any liquid refrigerant that may migrate into the compressor. If an evaporator coil is higher than the compressor at the end of a cycle and the compressor stops, liquid might drop causing it to collect on pistons or in the crankcase of the compressor. On some cool days, refrigerant can condense in the compressor if it isn’t being used. The crankcase heater prevents a compressor from trying to compress liquid refrigerant, thus resulting in mechanical failure. The heater is usually wired through a relay that opens the circuit when the compressor is in operation. Some manufacturers leave the crankcase heater energized all the time by wiring it to the line side of the compressor contactor. This can cause a compressor to become too hot when operating, thus opening the overload relay and stopping the compressor operation.
