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Air Conditioning Basics: A/C 101
Evaporator Operation: Lubricant Return
The Evaporator electric fans cause the
cool air contained within the conditioned space to flow over the fins of
this heat exchanger. Because the refrigerant is made to be colder in the
Evaporator than the surrounding cool conditioned air, heat is
transferred from the air to the refrigerant causing it to evaporate to
vapor form. This is the process, of course, that actually achieves air
conditioning.
During the evaporation process, the lubricating oil is also chilled
(it never changes phase; the oil always remains in liquid form). Thus,
what emerges from the Evaporator is the refrigerant vapor, slightly
superheated, and a cold flow of oil that coats the inside surface of the
suction line. This cold oil coating is dragged back to the Compressor
through the flow of the refrigerant vapor when it re-enters the
Compressor. Conventional compressors require this return oil flow not
only for lubrication, but also for cooling. It is apparent, however,
that the energy consumed in cooling the oil cannot be used to also cool
the air and is therefore a loss to the system.
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