No AC. Where to start?

[Purefection]

I found this: http://www.silveradosierra.com/how-...k-series-trucks-hvac-control-unit-t77522.html

I don't know what year your truck is so I hope the article applies.
Scroll down to about half way and he has a picture showing the locations of all the AC system switches. He also explains how to check each switch.
Beware that each switch is connected to the ECU, so if you try to jumper any of the switches with 12V power, make sure you have the right wire.

The whole article is actually very interesting.

Good luck!

Just read that actually. Just put my guage on the low pressure side with the truck off an I had 10 psi that slowly went down to 0

 

[96Z71ECSB]

Well that sucks. She's got a leak somewhere.
I've found that it's usually the schrader valves for either the low or high side filling ports.
Next up would be any O rings for the hoses in the system, particularly the O rings for the hoses at the compressor.
Lastly, it could be leaks in the compressor itself, the evaporator, or the condenser.

You'll more than likely have to put some freon in it to find the leaks.
Hopefully the leak will show itself immediately.

May the force be with you