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

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Servicing Practices
Non-condensables
Gases in the system which do not liquefy in the condenser are
contaminants and reduce the cooling capacity and system
efficiency. The quantity of non-condensable gas that is harmful
depends on the design and size of the refrigeration system and
nature of the refrigerant. Their presence contributes to higher
than normal discharge pressures and resultant higher discharge
temperature. Higher temperatures speed up undesirable chemical
reactions. Gases found in hermetic refrigeration units include
nitrogen, oxygen, carbon dioxide (CO2, R744), carbon monoxide,
methane and hydrogen.
These non-condensable gases infiltrate sealed systems in the following
manner:
• They are present during equipment manufacture or servicing
and remain due to incomplete evacuation.
• They are desorbed from various system materials or are formed
by decomposition of gases at elevated temperatures during
system operation.
• They enter through low side (below atmospheric pressure)
leakage points.
• They are formed from chemical reactions between refrigerants,
lubricants and other materials during operation. Chemically
reactive gases, such as hydrogen chloride, attack other
components in the refrigerating system; in extreme cases, the
refrigerating unit fails.
• They are introduced when connecting refrigerant hoses that
have not been properly purged.
Whilst designing, installing and servicing systems, technicians
should be aware of these routes to contamination, and adjust their
behaviour accordingly.
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