The crankcase heater warms the compressor crankcase during the off cycle. Crankcase heater is wired across the open contacts of the contactor. When contactor is de--energized, crankcase heater is on. When contacts are closed, no current flows through the heater because it is on the same line voltage side as the compressor. The heater is used to warm the oil, to reduce refrigerant migration, and ensure proper compressor lubrication

Crankcase heater is required is required on all low ambient applications where a MotorMaster is used.