The factory manuals are on this site somewhere but I cannot find them for some reason. The guy that posted them also put them here...
http://67-72chevytrucks.com/vboard/showthread.php?t=700011
I’d look for the wiring diagram for the HVAC in the manual. Too, there are probably diagnostic tables in it for a non-responsive control panel.
Mine is a 98 so it’s a little different, but I would think that the next step would be to see if you have power at the connector to the control panel. Not sure which wire it is, but would think you should see battery voltage.
If you have no power, then there’s an issue somewhere upstream of it. If you have voltage, then I’d suspect something with the panel. Check the ground coming from the panel as well. It’s probably a black wire in the connector.
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