A/C Issue

[truckman72]

Well its that time of year again. I have returned back to Kansas from Denver as I wrapped up the academic year, which means I pull my truck out from my parents for the summer. For those of you not familiar with Midwest Summers, they tend to be very sticky and hot; very different than the cool mountain climate of Colorado! Air Conditioning in Kansas in the summer is very necessary! Especially if you are overweight and get sweaty easily!

After some cleaning, firing up the engine, and turning on the a/c, I did some digging around and realized that the door inside the system will flip open to the windshield vents and close off the three front dash vents, but won't flip back to the other way on its own.

Any idea want might be causing this to happen? It is a 5.3L engine with the Vintage Air system. To be honest, I'm not to knowledgeable about this system as my Father put it in a couple of years ago while I was at school.