I've got a 2000 Dodge Ram Quad Cab 4x4 w/a 5.9. When I try to switch between Max AC, AC Defrost doesn't matter. The majority still blows out at the floor. I have Chilton's manual but it's no help on the vacuum lines on the back of this control. There either 4 or 5 lines, don't remember, all colored and 2 holes open. How do I tell if I have a vacuum leak or if the **** just needs replaced?

 

May be a vac. leak or balky diverter mode door. Is there any kind of noise, i.e. creaking, groaning, etc. when you try to switch modes?
Things to check:
1 Binding mode door
2 vacuum fitting at mode door/source
3 mode door vac. motor.
Hope this gets you started.
WC

 

I sounds like it's trying to switch or move but no changes in the air volume coming out of various locations. i.e. floor, defrost or panel. Are there any diagrams or pictures or cutaways showing these doors without going though all the hassle of removing the dash to get to the door? My shop manual doesn't show which vacuum lines are suppose to hooked up where.

 

https://dodgeforum.com/m_340929/tm.htm
That's a link Steve put up to a 2001 FSM. Download the file. It's very usefull even if you don't have a 2001. After downloading, look up in section 24, the heating-a/c system; controls. The yellow vac line is one that controls mode door for a/c.
WC