MODEL PCA090480WH
CHAPTER 2
SERVICE
Section 3: Refrigeration Basics and Service
March 2013
2-3
Proprietary/Confidential
Page 39
© 2013 Twist, Inc.
B.
Oil-Refrigerant
mixture
In vapor cycle refrigeration systems, oil and refrigerant mix
continuously. Refrigeration oils are soluble in liquid refrigerant, and at
normal room temperatures they will mix completely.
Since oil must pass through the compressor scrolls to provide
lubrication, a small amount of oil is always circulating with the
refrigerant.
Oil circulating in a refrigeration system may be exposed to both very
high and very low temperatures. Because of the critical nature of
lubrication under these conditions and the damage that can be done to
the system by impurities in the oil, use only the proper oil prepared for
the refrigerant and the compressor.
One of the basic characteristics of a refrigerant and oil mixture in a
refrigeration system is the fact that refrigerant is attracted by oil and will
vaporize and migrate through the system to the compressor crankcase
even though no pressure difference exists to cause its movement.
Upon reaching the crankcase, the refrigerant will condense into liquid,
and this migration will continue until the oil is saturated with liquid
refrigerant.
Upon
start-up,
excess
refrigerant in the compressor crankcase may
result in violent foaming and boiling action, driving all of the oil from the
crankcase and causing lubrication problems.
If excessive foaming is noted in the site glass, too much liquid has
returned to the crankcase and the system must be taken out-of-service
until a qualified technician can service the system. Failure to do so can
severely damage the compressor, creating added work and
considerable expense.
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