Techs pull a vacuum after any repair or install that opened the system, using large short hoses, Schrader cores removed and a micron gauge at the system rather than at the pump. A common target is below 500 microns, followed by a decay test: valve off the pump and watch whether the reading holds or climbs, which shows a leak or remaining moisture. Rushing the vacuum leaves non-condensables and water behind.
Pull a vacuum down to 400 microns, valve it off for ten minutes, and if it holds under 500 we'll release the charge.
A reading that climbs and levels off points to moisture boiling off; one that keeps rising steadily points to a leak.
Also heard as
- evacuate
- pull it down
- pull a deep vacuum
- evac
Related terms
Micron gauge
An electronic vacuum gauge that reads very low absolute pressure in microns of mercury during evacuation.
Non-condensables
Air, nitrogen or other gases trapped in a refrigeration system that will not condense at operating conditions.
Schrader valve
A spring-loaded valve core in a refrigerant service port, opened by the depressor in a gauge hose fitting.
Weigh in
To charge a system with a measured weight of refrigerant on a scale, set by nameplate charge and line set length.