Air Control Knob

[vtown00]

Not sure what I'll be getting into there, seems like it works when you want it to come straight out the upper vents, and then all of the other selections only push the air out the defrost window vents, so there isn't any floor, or floor/upper combo, they just come out by the windshield, any ideas as to what's going on before I tear the whole dash apart, seems kinda strange that it works on those selections but in a different area of the Expedition figured they just wouldn't work at all.