1968 plymouth valiant 100 a/c vacuum diagram (factory installed) with 225 slant 6

There were many part numbers applied to those 5-button switches, and they interchange. Whichever one you have bought will work in your car once you sort out the vacuum hose routing correctly. The diagram you need is in the FSM, chapter 24. Your type of factory air system was used from '65-'72. The heater water valve through '70 had two vacuum hoses going to it: one to open the valve and one to close it. The water valve for '71 and '72 had one vacuum hose; it was spring-loaded rather than having the "other side" vacuum hose. This didn't (and doesn't) necessitate a different switch, just different hose configurations. Once you go through, hose by hose, and make sure vacuum goes (and doesn't go) to where it should (and shouldn't) be in every button position, your system will work correctly. It's tedious to figure out, and while you're in the middle of it it seems like it'll never work correctly, but keep at it, and it will.