Where the can I find the vaccum leak that makes my vents stick on default (a.k.a.) defrost position? Sean, I'm lookin' at you!

 

Oh crap, I've got people asking for me by name now. The vacuum line for the climate controls enters the passenger compartment near the heater box, it's a plastic line. It should be hooked up directly to the vacuum tee on the intake manifold. The plastic line tends to get brittle and break. I'm not sure of the exact routing of the line inside the cab, so you would have to trace it inside. Most of the time the problem is under the hood.