When I saw the first few seconds of one of your videos, I thought it was a little 'wierd' and clicked away but they kept coming up and I see you really know your stuff. I watched a few of them on AC recharge/repair and am taking you up on your offer to 'ask Scotty'. I'm not a major mechanic but pretty good with clear small jobs.
I have a 1996 Corvette and the AC was working fine last year. This year, it started blowing hot air. The compressor didn't even turn on and there was no pressure so I bought a set of guages and added some 134a. Then, the compressor started up and cycling. Soon it stopped cycling and stayed on permanently (low about 35 psi, high about 250psi) but blowing great cold air. I found a video on youtube with that exact symptom - something about one of the switches must be bad.
But since it started out cycling, I'm not so convinced. Also, the schrader valves (both!) leaked profusely when I took the caps off. So I bought a compressor based vacuum and some schrader valves, more 134a and oil and plan on evacuating the system and recharge.
In the above testing, the pressure was holding for at least 20 minutes. I was wondering if I really should bother evacuating or just add some UV dye first to see where any leak is?
I've gotten some help from the corvette forum and a friend who is smart car guy and they say that if I'm evacuating the system, I probably should replace the dryer and the 'orifice valve'. Your video's don't mention that - but you do say that I should keep the vacuum on for about an hour to dry things out. Comment?