47-55.1 Any AC experts?

[TX3100Guy]

While this issue was not with my Chevy truck, I suspect there are multiple AC experts here and hope you guys can offer some useful suggestions on what I should do next.

I have a Classic Air AC system installed on another old classic car. It was blowing cold for a minute or two and then blowing hot. Last week while taking it to a car show, it blew cold for five to ten minutes, then it shut itself off (literally stopped blowing all together). Since it was nearly 100 degree's the wife and I opened the windows for some hot breeze. Maybe another ten minutes later I tried turning it back on (I had turned it off when it stopped on its own). It would only blow hot air.

A friend/mechanic suggested that I had a bad expansion valve, so I purchased a replacement and pulled the evaporator coil/fan unit out of the car and replaced the expansion valve. I then used my vacuum pump to draw a vacuum for over an hour, shut the manifold valves, let it sit for several hours with no loss of vacuum. I then ran the vacuum for another hour before I began adding R134a with the car and AC running. Shortly after allowing the refrigerant to enter via the low pressure side the compressor clutch engaged and I thought things were going well. Then I noticed that the R123a can was icing up and the low side pressures were nearly 50 and the high side was barely 20-30. Then the evaporator fan shut off, the compressor clutch de-engaged and no R134a was entering the system.

I closed all the manifold and hi/lo valves. I had a suspicion that the binary switch was defective, but after removal and testing it appears to work properly (although I'm open to suggestions if this could be the culprit).

My current thought is that the expansion valve might not have been the problem at all. Couldn't it be that the compressor has issues and that when its blowing hot, it because the clutch has disengaged too soon? I can't explain why the system shuts off, unless the binary switch is sensing too high of pressures and is shutting things down. As you can see, I'm grasping at straws for a solution.

At the moment, I have evacuated the system yet again and have it sealed off under vacuum overnight to ensure there are no leaks. Any thoughts are appreciated.