Isolating a system under vacuum and watching the micron reading to separate a leak from moisture.
After evacuation, the vacuum pump is valved off and the micron gauge watched for a set time. A reading that rises and levels off suggests moisture or oil still boiling off: keep evacuating. A reading that keeps climbing towards atmospheric pressure suggests a leak: air has no equilibrium point short of atmosphere.
The acceptable rise and the hold time come from the equipment manufacturer or your employer's procedure.
Exam work areas
B · Tools, piping and refrigerant handling