Many many days later I found the trouble. Wire harness corrosion on a hidden terminating connector wrapped inside the harness directly under the junction of the AC unit and the blower. The circuit that feeds 12v to the key-in switch only had 5v even with the fuse for the circuit removed. Connected a tone generator and used a tracer to find the signal stopped midway in the harness. Invaluable tool this TestUm Tonax and ResiTracer has become. Looks like another few days till repair, as I will have to remove the blower to get full access to repair the harness wires. Will post pictures soon. Looks like the source of moisture is from a coolant leak, likely from the heater core as the dried up corrosion is baby blue colored.
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