AC/heater dashboard vents

[Al59]

Air will blow out from under the bottom of the dash and the windsheild defroster but not out of the top dashboard vents. Nothing changes when selecting different positions at the switch.

[ggcatt]

There are several threads on this and the Chevy Astro site that deal with your problem. You likely have a vacuum leak at the engine, either the connection or the actual hose. Check there first.