Mike has answered all my past questions but here are some more. You guys probably don't believe that I was a diesel fleet mechanic and shop superintendent for 30 years. I think I have forgotten more than I ever learned and this new stuff has just passed me up since my retirement. Question: I have a vacuum pump that sucks 20 inch of vac. Is that enough to vacuum an AC system after disassembly? At NAPA buying my evaporator and thought I would just buy some compressor oil while I was there. There are 4 different kinds in the same brand. Which type do I use? I really should bring this truck up to mike and have him show me some spots to hunt chuckars with my bird dog before I am to old to do that also.

I typically pull about 25-27 inHg with my pump which is fine. I would just run the vacuum pump longer to draw the moisture out. Then shut it all down and leave the gauges on and check for leaks. It should hold vacuum over 12 hours without change. As for compressor oil I typically call the NAPA store and have them look it up for the vehicle. But I know my 2002 takes PAG 100 oil and it a holds of 7.1 ounces of oil to the compressor. So just pull the drain plug and drain out and reload. Just like a oil change.

thats not a very good vacuum BUT heat is your friend, you are trying to boil of the water/moisture in the system so heat and extend the time and could purge a few times with nitrogen or refrigerant (not politically correct) and re evacuate.

You can go down to an Autozone or Advance (or probably O'Reilly, too) and "rent" a pump that'll pull a pretty hard vacuum for about $150. They refund  you when you bring it back.