468
Modern Refrigeration and Air Conditioning
• To add oil.
• To evacuate the system.
• To make it easier to replace driers, compressors,
evaporators, and refrigerant controls.
• To recharge the system.
Most refrigerators with hermetic compressors do
not have built-in service valves. Some have fittings to
which valves can be attached for service operations.
The valves are removed from the fittings when the ser-
vice work has been completed.
Some systems have neither service valves nor fit-
tings on which to attach valves. On such units, pierc-
ing valves or process tube adapters must be installed
to provide a means of attaching a manifold gauge or
other service equipment.
Systems with Valve Adapters
Valve adapters provide another method of con-
necting gauges and charging cylinders to a hermetic
system. Figure 19-18 shows one part of the adapter fas-
tened to the compressor dome. The other part of the
adapter has a removable valve stem, Figure 19-19, that
can be attached to the valve, as shown in Figure 19-20.
The valve stem operates the small needle valve
mounted in the part of the adapter installed on the
compressor. The part of the valve adapter containing
the valve stem also has one or more ports for attaching
gauges or service hoses. Synthetic or copper gaskets
between the valve assembly and compressor fitting
seal the joints.
Brazed or
welded joint
Valve
Valve
attachment
threads
Compressor
housing
Screwhead
Goodheart-Willcox Publisher
Figure 19-18. Service valve adapter installed in the dome of
a hermetic compressor. A valve attachment must be fastened
to the adapter before the valve can be opened. If it is not,
refrigerant will escape.
Handwheel
Port
Needle
valve
drive
Valve stem Valve attachment
threads
Goodheart-Willcox Publisher
Figure 19-19. A service valve attachment like the one shown
is installed on a valve adapter. The hand wheel is attached
to the valve stem and needle valve drive, which operates the
needle valve in the adapter.
Valve
Valve
adapter
Compressor housing
Gasket
Needle
valve
drive
Valve
stem
Port
Handwheel
Goodheart-Willcox Publisher
Figure 19-20. This cutaway shows a valve attachment
connected to a valve adapter on the housing of a hermetic
compressor.