I have a problem with my 2003 astro van that sounds similar to a former post in that I only get air flow thru my defroster vents when either the a/c or heat is turned on and nothing thru the dash vents. In addition to this there is a rattling/rolling sound coming from the vent when the vehicle moves forward or reverse. Is there something broken inside the ductwork besides the possibility of a vacuum line problem?

 

Sound like something might have been dropped into the duct work. A nut or two could be making the rolling noise and prevent movement of the air flow doors. If you can find a place to rent one, a borescope would let you look around inside without taking things apart.

 

I have the exact same problem w/o the rattling. Air comes out the window defrost and the foot area but not the vents. I used to think such things were the result of and ongoing communist plot but of course I have updated to -- al quida plot;-)
Please let me know if you figure it out. patrick

 

I have the same problem found a broken vacuum line up front right side and replaced it, but still don't get air through the dash vents.

 

Start from scratch and replace all vacuum lines and your problem will be solved.

 

There's also a chance of a bad vacuum line in the area of the intake manifold. It's common on Astro's for this to get cooked by engine heat.