97 Aero. Just recently experienced this weird issue. Had the AC on for a warm day and heading down the freeway at 70mph. The AC is kicking out some nice cool air. Noticed that when the van was heading up a slight grade, the air speed comming out of the vent would slowly diminish until no air came through the vents at all. As soon as the van leveled out or started heading downhill, the vent air speed would pick back up and blow normally. This happened repeatedly. Is this a blower issue? Vent door issue? Something else????? Since the van was traveling at speed, I could not tell is the blower was still blowing when I was experiencing no air out of the vents.