After opening a stem for repair I always put on the Vac pump. Will run it to at least 500 microns before isolating and confirming no leak. If the system was open for installing or replacing a drier than I know a lot more moisture got in. It SEEMS that the pump dowm takes longer to get the moisture out. Question to you techs: When I isolate the pump at 500 microns (got a good "Val-Chek") and it still creeps up, I assume there is still moisture in the system that needs to be boiled off. SO.... I keep the pump running until I am certain I've fully boiled everthing off. EVERYONE else at my company does NOT. They typically pump it down for, say 15-30 minutes and think its good enough. Most don't have a micron gage. They say "time is money" and I'm just wasting time. I wish to be CERTAIN there is NO leak AND got all the air + moisture from the system.
PLEASE give me your feedback and what procedure(s) work for you.