Manual for Refrigeration Servicing Technicians - UNEP - Division of ...

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Servicing Practices
Leak detection
RAC systems are designed to operate adequately with a fixed
charge of refrigerant. If it has been determined that a system has
insufficient refrigerant, the system must be checked for leaks, then
repaired and recharged.
Refrigerant leaks are caused by material failure. The mechanism that
creates the material failure is normally attributable to one or more of the
following factors:
• Vibration – Vibration is a significant factor in material failure and
is responsible for “work hardening” of copper, misalignment of
seals, loosening of securing bolts to flanges, etc.
• Pressure changes – Refrigeration systems depend on the changes
in pressure for their operation. The rate of change of pressure
has different effects on the various components in the system,
which results in material stress and differential expansion and
contraction.
• Temperature changes – Refrigeration systems frequently consist
of different materials of differing thickness. Rapid changes in
temperature result in material stress and differential expansion
and contraction.
• Frictional wear – There are many cases of frictional wear causing
material failure, and they vary from poorly-fixed pipework to
shaft seals.
• Incorrect material selection – In a number of cases, inappropriate
materials are selected e.g., certain types of flexible hoses have
a known leakage rate, and materials that are known to fail under
conditions of vibration and transient pressure and temperature
changes are used.
• Poor quality control – Unless the materials used in the refrigeration
system are of a high and consistent standard, changes in
vibration, pressure and temperature will cause failure.
• Poor connections – Poorly made connections, either brazed joints,
screwed connections, or not replacing caps on valves, can allow
refrigerant to escape.
• Corrosion – Exposure to a variety of chemicals or the weathering
can result in a variety of different corrosion modes, which decays
the construction material resulting in the eventual creation of holes.
• Accidental damage – Accidental mechanical impacts to
refrigerant-containing parts can happen under many
circumstances, and therefore it is appropriate to ensure that all
parts of the system are protected against external impacts.
Designers, installers and service
and maintenance technicians should
all be aware of these phenomena,
and always check to see if any are
occurring or leading to leakage
whenever possible.
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