Many larger refrigeration and air conditioning compressors — usually over 5 horsepower — have forced oiling systems. These compressors contain an oil pump located at the end of the compressor’s crankshaft (see Figure 1, top). The crankshaft is actually connected to the oil pump and supplies power, which turns the oil pump. The oil pump is keyed into the compressor’s crankshaft.
Oil pumps force oil through drilled holes or oil galleys in the crankshaft and deliver it to bearings and connecting rods. The oil then drops to the crankcase to be filtered and picked up again by the oil pump. Smaller compressors usually have some sort of splash-type oiling system. These systems may have an oil scoop that scoops and flings the oil throughout the crankcase, causing an oil fog as the crankshaft rotates.