Where do the dash vents lead if I need to retrieve something

Hello, unfortunately, it seems as if you may have debris (marbles) caught in the plenum of the system, which could restrict air flow and movement of the blend doors. If you're lucky, you may be able to get inside through where the cabin air filter is and try to see if you can access and remove any of these foreign objects. Beyond that, only tear down of the dash to get into the plenum would be possible.