Bought car and the HVAC vent selector knob had no effect. Weak air came out of, it seemed like all the vents at the same time.

Found a youtube video showing the fix is the black plastic vacuum line feed passing by the bottom side of the engine battery is easily broken due to battery acid fumes and any mechanic who is not gentle in that area.

Fix: Removed battery. Located remnant of line on passenger fender wall at the vacuum T.

Used knife to slice open the main thick wires loom electric tape wapping coming from large electric fuse box which goes towards the firewall. This is buy the battery. Inside, I found the other broken end of the black plastic tiny straw like vacuum tube.

Removed any brittle ends of both tube broken ends. Took a small piece to an auto parts store counter clerk and asked for a short length of vacuum rubber hose that will fit over the plastic tube.

Cut rubber hose to length needed. Spit on all ends and inserted hose onto tube ends. Tested with battery temporarily installed and engine running. Now HVAC vent knob works Perfectly, with vacuum restored to door actuator. Electric taped wire loom back together and secured hose so a rough battery replacement mechanic won't catch and break it again.

Take care.