[GMC Canuck]

good find on the water valve. Any time the heater and A/C try and fight each other, the a/c always loses. The low side shooting up to 65 isn't a major concern, it could be just the belt/clutch slipping so the compressor stops pumping. Did you happen to notice the discharge pressure when this was happening? I would watch your discharge pressure. over 200 is getting a little high but with 95 degree ambient not abnormal. If you have air in the system your discharge pressure will be really high.

I would be careful using compressed air to flush a system. Make sure you have some sort of drier or water separator on your compressor. Water even in small amounts can cause large problems. If there is water in the system some time on a vacuum pump will boil/evaporate it out of the system but it does take quite a while. Same goes with most commercial flushes, it should evaporate.