2005 Chevy Astro

It sounds like 2 seperate problems but there is a possibility that the ac control head may be the culprit. For the blower speed problem, there is a high blower relay that has usually gone bad when there is no high speed of the fan. As far as no air through the vents, this is most likely a vacuum loss problem. Near the battery is a vacuum cannister. You have to look down behind the battery to see it. It has one vacuum line going to it. Take this line off with the engine running and see if you have vacuum there. If not trace the line back towards the engine to see where the vacuum loss is.

I started out saying it may not be 2 seperate problems. Both of these issues may be control head related. I think I would check the vacuum to the cannister 1st and if you find a vacuum leak, then there is most likely 2 concerns. If the vacuum checks out good all the way, then the control head is more likely.