65 Dart Heater AC Fan Problem

retractable said
I have seen differences in the elc connections on the vac switches. The picture with the darker connections and small screws holding switch together came out of my 66 barracuda with a.c.. the other vac switch has a different elc connections. I don't know what the difference is. I tried that switch in my 66 Barracuda and the a.c. did not work. This might be your problem.

View attachment 1715369554

I believe you're right, retractable.
The two push buttons on the original switch went to heat and defrost, or C1/C1B and C4A in the wiring diagram. The new switches have three terminals. I guess you'd have to look at a later model wiring diagram to determine which terminal(s) on the new switch should go to which wire, or just try the various combinations with a voltmeter.