Thanks to those who offered suggestions on my A/C's bad habit. Sadly, these suggestions did not solve the problem. However, having been fed up with having my dash apart with voltmeter in hand while trying to drive--I broke down and went back to testing. Here is that which I learned and if it saves one person the hors of frustration I suffered, the efforts of my labor are worthwhile.

Seems the manually controled AC system on these cars routes voltage through the resistor pack only on the three lowest settings. On high (="4"), a low-current signal is fed to a standard Bosch type relay mounted just above and to the right of the big green relay one sees when the glovebox is removed. This relay is the "high-speed fan" relay.

And mine was bad. I took it apart and found the spring had failed so that when not energized, the contact would sometimes make a connection and sometimes not. But it would never return to the off pole, thereby never allowing the speed switch to work unless a harsh bump forced the issue.

A new $5 relay and I am back to full control.

I still do not understand why the "0" setting does not turn off the compressor but that is a mod for another day. I have control over the AC and I'm happy for now.