An air conditioner crankcase heater is an electrical heating device that is installed in the compressor of an air conditioning unit to prevent refrigerant from migrating into the compressor oil and causing damage. The crankcase heater is designed to keep the oil in the compressor warm and prevent it from becoming too thick and viscous during cold weather. When an air conditioning system is not in use for an extended period of time, the oil in the compressor can cool down and become too thick to circulate properly. This can cause damage to the compressor and reduce the efficiency of the air conditioning system.