2000 Chevy Astro AC/Heater Controls

The heater and AC work just fine, as does the blower motor. The problem is that I don't have any control over where the air goes. It almost seems as if a supply duct has come loose, and all the air is being dumped somewhere behind the dash area. I cannot direct air to the defroster, the dash vents, the floor area, etc. But I can hear the blower running & I can hear air movement. Is there a chance there is a vacuum leak controlling the vacuum motors for the various functions of the controller? What should I look for?

Thank you!