Well the pushbutton controller does two most basic tasks. One is turning on the compressor relay and the other is commanding the blower controller. I'd pick one and see if it has any activity. The clicks you hear could be the other less conspicuous task of commanding the vacuum switchover valves. If it is doing that it isn't totally dead.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician