The problem with a pressure cooker in a vacuum situation is you cannot see what's going on and the gage is only an indicator of what's happening.
The solutiopn"boils" over at different temps. and vacuums.
Pickle jars alone work fine and I am not going to get involved in another debate.THere are quite a few threads/ posts on this subject.
I make most of my pens out of Saguaro Cactus Skeletons, very old, very dry, very unstable. I have tried everything, jars, pressure cookers, 2 qt paint pots and didn't find anytrhing that could hold a high vacuum for a long time till I bought a vacuum chamber on ebay. $40., but it works like a champ. A little secret I discovered is to use vacuum grease on the gasket. You can order vacuum grease from any lab supply source. Maybe I'll take a picture of my set up and post it here, if I can figure out how. Good luck!
Mark, here is that picture of my setup. The Pyrex vacuum chamber is a piece of lab equipment I found on ebay. It did take about 6 months to find one I could afford but worth the wait. Simple air conditioner pump for the vacuum and that all important tube of vacuum grease in front.
I don't have a vacuum gauge on the chamber but my pump pulls 22 inches so I just run it till no air is exhausting. I do have a vacuum gauge on my 2 qt paint pot so I can get a reading off that and I could put a gauge inline... but this isn't rocket science.
Sorry, I didn't see the AC question. I don't know what size unit it came from. It's also an ebay item. It's a rebuilt pump that is supposed to pull 21 inches although it pulls 22 on both of my gauges. Of course both my gauges are ebay items to, so how accurate any of this stuff is, is a mystery. It does do what it's supposed to do, make bad wood into good wood.
THere is no vacuum pump in an AC unit but a compressor can be used as a vacuum pump.
HVAC techs use vacuum pumps to pull a suction on HVAC lines to make sure there is no moisture or debris when changing out a compressor or installing a split system.