The
purpose of a vacuum pump is to remove moisture and
air from an A/C-R system.
Modern systems are built tighter and charges are more
critical. That means these systems have a greater
sensitivity to moisture and other contaminants, making
thorough evacuation more important than ever before.
Moisture in a refrigeration system, directly
or indirectly, is the cause of most
problems and complaints. First,
moisture can cause freeze-up in a system. Moisture is picked
up by the refrigerant and transported through the
refrigerant line in a fine mist, with
ice crystals forming at the point of
expansion.
“Freeze-up” is not the only problem caused by
moisture. It can also result in
corrosion, the effects of which are not
apparent until the real damage has occurred.
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Moisture
alone is bad enough, but combined with
refrigerants containing chlorine,
hydrochloric acids can form. These
greatly increase the corrosion of metals.
Also, refrigerant oil rapidly absorbs moisture.
Water-formed acids combine with the
refrigerant, forming a closely bonded
mixture of fine globules.
The effect is called sludging and it
greatly reduces the lubricating
ability of the oil.
A vacuum pump removes troublesome moisture by
lowering the pressure within the system and vaporizing
(or boiling off) the moisture, then exhausting it along
with air.