Where does the Vacuum connect to the HVAC system in a 1995 S10 with a 2.2 engine?

There is probably a large harness coming through the firewall below the clutch master cylinder. It will have a thin plastic tube branching out of it just below the clutch cylinder (or where it would be if manual). A small rubber hose from the intake manifold which has just passed through a check valve and teed into two. The small branch goes to the thin plastic line from the harness. The remaining rubber hose goes to a vacuum tank hidden in the fender space.