On the high fan, the high speed relay located under the hood near the fan may be blown. As far as your vent operation, on my GN it was slow to react when I turned on the AC. It would blow as you describe your system. Out the top and bottom. I got tired of putting up with it so I fixed it so all temps, heat and cold, blow out the dash vents. I used a piece of paint mixing stick to jam the flap located inside the center two vents on the dash. You open the flap in there and prop it open.