You have a vacuum problem. With no vacuum on the master switch nothing works EXCEPT defrost which is always HOT.

To test, verify the vacuum on the temp switch at the base of the servo unit (in the engine compartment). Both sides of the switch should have vacuum. It goes from there to the pushbuttons and the master switch.
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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician