I have a Chevy g20 1993 5.7 extended van. 148k miles and runs relatively good. Only thing that’s stumped me so far is the AC. It works and gets hot out the defrost. But does not really get cool or come out the front vents. I’ve changed the check valve and looked over the lines around it and the hoses seem to be in okay shape. Any other ideas of things to look at?

 

It falls back to defrost as default when there is a vaccum leak for the vent controls. You need to remove the dash and fix the vaccum lines there it you are unlucky. But mostlikely it is just a vaccum line from the vaccum ball under the hood to the PCV valve or after the valve. Replace them all. Video is in german, but you get the point