'94 E420 A/C Erratic Behavior

[weilands3]

The first $$$Costly behavior!

In hot summer weather, typical of Southern Oregon, the A/C will not function. I try to go to all buttons on the console as well as move the temp.wheel to and fro. The a/c will not kick in.
After car has been turned off and restarted the a/c will work if the a/c buttons have been selected and the temp.wheel is in 65° or less setting.

To fix our dealer took $750 to replace several switches and filters etc.!

The problem is not solved if I switch from a/c to economy or off with engine running. Sometimes a/c is not needed even here!
It was suggested that I allow more time after switching back and forth.
It was suggested that I not switch at all when it is working?

Any thoughts would be appreciated.
Answers please?