Atmospheric pressure is about 760,000 microns, and a properly evacuated system sits at a few hundred, far below what a compound gauge can show. The micron gauge is the only way to prove that air and moisture are out and that the system holds vacuum. It should connect at the system end, away from the pump, and its sensor must be kept clean of oil.
Manifold says 30 inches, but the micron gauge says 4,000, we're nowhere near done.
Also heard as
- electronic vacuum gauge
Related terms
Pull a vacuum
To evacuate a refrigeration system with a vacuum pump, removing air and moisture before charging.
Non-condensables
Air, nitrogen or other gases trapped in a refrigeration system that will not condense at operating conditions.
Gauges
The manifold gauge set techs connect to service ports to read system pressures, saturation temperatures and charge.