My 01 sierra has no air. I first thought maybe the refrigerant leaked out and needed charged. The Compressor is not kicking on, I jumped the pressure switch to see if that was maybe the problem and no difference. I looked under neath at the compressor and the belt is very loose, the tensioner is not engaging. 1 ( is this electric and energizes to tighten the belt or is she broke?) I then used a socket wrench to manually put tension on the belt thinking the belt is not engaging the compressor but No. Any ideas??

 

The tensioner only works onspring load. So if it is loose then it is probably broken. Beware... they are high dollar. Bout 80 bucks. Try that and see. If its not ur problem then let me know.