I have a 2004 KJ with a minor issue. Sometimes the air will blow out the top or bottom, even though I have it set to blow out the front vents. This only happens at fast highway speeds (maybe 70+). It never, or very rarely at least, happens at city speeds.
The only explanation I can come up with is that whatever is used to route the air is vacuum controlled. Since you have less vacuum at high speeds, this could explain what I'm seeing.
Does this thing actually work on vacuum, or can someone explain how it does work? Any tips on troubleshooting would be appreciated.