110
Chapter 6
I.
Control of Liquid Migration to
the Compressor During
Shutdown
A. Liquid Refrigerant Mitigation to
Compressor During Shutdown
Liquid refrigerant migration to the compressor is a
natural occurrence within refrigeration and air con-
ditioning systems (see Figure 6-1). The amount and
severity of this liquid refrigerant migration depends
on several things, such as the size of refrigerant
and
oil charge and the length of shutdown interval.
This discussion shows that while Tecumseh com-
pressors enjoy a fine reputation for reliability and
long life, there are application safeguards that can be
employed to increase compressor life and eliminate
unnecessary service calls. These action photographs
(see Figures 6-2 to 6-4) were taken in the engineer-
ing laboratories of Tecumseh Products Company. A
five ton split air conditioning system was used with
a four inch sight glass installed in the compressor
housing. The condensing unit and evaporator sec-
tion were connected by approximately 25 feet of
suction and discharge tubing. The first internal view
shows the system shut down for a week-end. The
temperatures of the compressor and evaporator are
the same, 76°F.
Even at this condition, the fluid in the evaporator,
which is mostly refrigerant, has a higher vapor pres-
sure than the fluid in the crankcase, which is mostly
oil. This difference in vapor pressure acts as a driving
force for the refrigerant to migrate to the crankcase–
to become absorbed in the oil until the pressures are
equalized and saturation has been reached.
Figure 6-1.
Liquid refrigerant migration to compressor.
High Pressure Gas
High Pressure Liquid
Low Pressure Liquid
Low Pressure Gas
Fan
Fan
Evaporator
Condenser
Compressor
Expansion Device
Filter
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