A crankcase heater is a resistance heater in a compressor used in an air-conditioning system, heat system or chiller system. The crankcase heater helps to keep the refrigerant from mixing with the oil mixture in the system; preventing explosions.
Refrigerant tends to migrate to the compressor's crankcase. This is a problem because when the refrigerant mixes with the oil mixture it can cause a violent explosion. It can also cause foam to come up through crevices and broken valves. One way to stop the refrigerant from migrating to the crankcase is by attaching a crankcase heater. The crankcase heater then holds the oil in the compressor's crankcase at a temperature higher than the coldest part of the system. This helps to ensure that refrigerant will be vaporized and driven back out of the suction line.