I have a 1997 4.6. While driving around town the other day I had my a/c on, worked fine. Went into a store and no a/c after that. The clutch does not engage. Fusses are good. Compressor should be good, I replaced it last year and I know the clutch spins freely with no grinding. I pushed on the front to check if it was the gap keeping it from engaging but it still didn't. Pressure in lines are good. What switches should I check and how should I check them eg. positive lead to wire, negative to ground? Am I looking for a result of 12v in all of them? I checked the clip on front top of compressor but only got 25mv. Also any ideas on best way to check compressor ground and what result am I looking for on the volt meter for that? Also the last time I did any work to my truck was when a piece of foil from an oil jug went into the valve cover so I had to move those wires on the top and disconnect the a/c compressor to get to it. Sorry for so many questions its been a while since I learned and applied electrical diag.

Thanks for the help.

 

Electrical schematic: