As noted earlier, the Compressor draws in the refrigerant gas on the Suction side from the Evaporator through the suction line. However, because Compressors are precision machines whose mating and running parts operate at extremely close clearances and often at very high relative velocities and loads, they require a continuous and adequate supply of lubricant. Therefore, oil is added to the refrigerant that circulates through the vapor cycle air conditioning loop. Thus, the Compressor not only compresses the refrigerant gas, but also pumps its own lubricant.

While circulating lubricant is vital to the survival of conventional Compressors, the lubricant degrades the performance of both the Evaporator and Condenser because it partially coats and therefore insulates their inside surfaces with a film of oil. Further, the flow of lubricant within the refrigerant causes cycle efficiency to drop because energy is wasted on circulating the oil that is occupying refrigerant volume. Generally, about five percent of the total flow through the loop is taken up by the lubricant.

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