Digital climate controller

[92gmc]

Howdy folks - Lookin for an AC Guru... I've got a 92 - 350 with ac/heat problems. A week or so ago the control panel in the dash quit - no lights - nothing - no ac/heat/fan. The next day it was working then it quit again. I checked the fuses and the power going to the control head. I made the assumption that the head was bad and ordered a new (Used) one.

Still nothing. Before I return the new used one I wanted to see what I was missing so I'm asking for advice. The wiring diagram I have is very basic so I haven't been able to figure this out.

I don't believe it is a compressor/freon problem because of the way it quit but... I've been wrong before.