ronobrien
Guru
To add to this, in a vacuum, water (moisture) will boil. The vacuum pump will suck out the refrigerant and some of the oil. It will boil the water and that vapor will be pulled out too.
I do a lot of my own work on classic cars. Because I live in the valley of the sun all of my classic cars have AC. Generally, if I am going to pull down an AC system with a vacuum pump, I will hook the vacuum pump up and let it run all night. I have my own vacuum pump. And I know there is a rental place not too far away from me that will rent one. Which may be a solution.
I have never worked on a R22 system. I would want to be familiar with operating pressures before doing work.
Good point about the pressures. Those will vary with refrigerant type and to some degree with the system design.