Crankcase heat is common in air conditioning (cooling) systems where R-22 has been used for many years. The home owner often shuts off the disconnect to the outdoor condensing unit for the winter, leaving the compressor without crankcase heat. If the homeowner then starts the unit without some time for the heat to boil the refrigerant out the oil, damage likely occurs to the compressor. On start-up, the crankcase pressure reduces as soon as the compressor starts to turn. The refrigerant boils and turns the oil to foam. The oil and refrigerant (some of the refrigerant may be in liquid state) is pumped out of the compressor. Valve and bearing damage may occur and the compressor may be operated with a limited oil charge until it returns to the crankcase from the evaporator.
