The crankcase heater is used to prevent the accumulation of liquid refrigerant in oil which occupies the compressor crankcase. Compressor oil is said to have a high affinity for the majority of refrigerants. That is, it absorbs the refrigerant vapor or liquid easily. He absorbs the refrigerant vapor is especially well when the oil is cool. During shutdown, the refrigerant naturally migrates towards the coolest place in the system. While the compressor is still hot, the most likely place for a refrigerant for migration is the evaporator. How cool compressor, however, refrigerant will migrate to the oil in the crankcase of the compressor.
When the compressor cycles, crankcase pressure to rapidly drop to the level of the suction pressure. This leads to liquid refrigerant, mixed with oil, boiled suddenly and violently. The foaming of the oil-mixture of the refrigerant then gets into the combustion chambers, slugging compressor, causing oil to leave the compressor.
Oil starvation can cause excessive wear on the compressor, heat, and even arrest. In addition, the refrigerant dilutes oil, reducing its lubricating properties.
The accumulation of refrigerant in the sump at the time of shutdown can be minimized by maintaining Carter warmer than the rest of the system. The heaters are installed inside or outside the housing on many compressors for this purpose. They are normally included by the manufacturer as part of the compressor. Shown left is a heater that attaches to the bottom of the crankcase, outside of the compressor. "Immersion heaters" in the center is inserted in the housing. Pipe where the heater is inserted sitting right in oil. The smell, or "belly band" heater right, wraps around the base of welded hermetic compressor.
The crankcase heater is usually controlled so that whenever compressor off. It must be activated no later than 24 hours before the start of the air conditioning system that had closed for the winter or any other longer period of time.
The crankcase heater low-cost maintenance and operation. Heater on the residential system uses so much electricity, 75-watt light bulb. The crankcase heaters are considered a "must" in many applications...
Refrigeration 
