950-0265revC - 22 - November 30, 2020
THE IMPORTANCE OF DEEP VACUUM
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.
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.
