Quoting geno:
now that your system is exposed to the air, change your dryer. if the dryer is exposed to the atmosphere for more than 30mins, its ruined. why? because there is desiccant inside that removed moisture from your ac system. . . . if you dont change the dryer your system will have moisture in it which can clog your expansion valve(the moisture turns to ice and gets stuck at the valve).
You are absolutely correct on this. However, I don't know if the 30 minute rule is necessarily so critical. I pulled the AC bits off 195/2000 (which had lost all charge after the front end collision) to complete the system on 464/1000. The system was open and exposed to air for the better part of two weeks. Granted, this was in Phoenix, in late summer, but still.
Installed the new o-rings, added the oil, connected everything up, and had a shop test the system for leaks. 220psi nitrogen charge held all day. They put a vac on the system and charged me up with r134. AC blows 45* according to the meat thermometer stuck in the center vents.
I wonder, did the dry, Arizona heat restore the dessicant in the dryer? Does pressurizing the system with nitrogen (inert) force any residual moisture out of the system when a vacuum is then applied?
I am no expert by any means, but from what I found in my research on the subject and in talking to local AC experts, the pressure differential is the heart of the whole system. If it's not just right, you won't get peak cooling.
Appreciate your stepping in to help out. This time of year, AC is super important.