Vacuum line

This information is based on 4.3L engine - 2 wheel drive - - I did not see any details so I’ll have to assume.. Vacuum amplifier (round black ball) is inside the drivers fender - at the rear .. It’s difficult to get to - that’s the vacuum source for HVAC control.. Vacuum supply going to that part is just to the right of the brake booster. Look at the vacuum hose routing diagram under hood. Good luck!