MODEL PCA090480WH
CHAPTER 2
SERVICE
Section 3: Refrigeration Basics and Service
March 2013
2-3
Proprietary/Confidential
Page 45
© 2013 Twist, Inc.
When a leak is located, mark it. When leak testing is completed and all
leaks have been located and marked, vent the test pressure gas. If a
leak requiring brazing is found in the high-pressure side of a system
containing a refrigerant charge in a location that cannot be isolated,
remove the refrigerant in order to make repairs.
When pressure has been removed from the area where the leak is
located, repair the leak. It may be necessary to re-braze fittings,
replace gaskets, repair flare connections, or merely tighten connections.
When all leaks have been repaired, pressurize the system again and
repeat the leak testing process.
Pressure leak testing is necessary to locate individual leaks. In order to
determine if the system is free of all leaks, a vacuum test is helpful.
After repairing all known leaks, draw a deep vacuum on the system with
a good vacuum pump. Reduce the pressure to 1 psia or less (the
vacuum registered on the test gauge will vary with atmospheric
pressure), reseal the system, and leave it for at least 12 hours. Any
leakage of air into the system will cause the vacuum reading to
decrease. (Changes in ambient temperature may cause some slight
change in pressure.) If an air leak is indicated, again pressure leak test
the system and locate and repair the leaks.
G.
Brazing Refrigerant Lines
The refrigeration system must be leak free. Clean and burnish the
tubing bright before brazing. Care in cleaning is essential for good gas-
tight connections. Give particular attention to preventing metal particles
or abrasive material from entering the tubing.
A suitable low temperature brazing flux that is fully liquid and active
below the flow point of the brazing alloy is required. Brazing fluxes are
quite active chemically and must be kept out of the system. Only flux
the male connection and use only enough flux to adequately cover the
surface.
When heat is applied to copper in the presence of air, copper oxide is
formed. This oxide can be extremely harmful to a refrigerating system.
To prevent its formation, sweep an inert gas such as dry nitrogen
through the line at low pressure during the brazing operation. Always
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