AC Controls question

[jtminton]

I just got a new set of AC Controls (thanks pjmoreland!) for my 72 C-20 and had a question about the vacuum port thing on the top of the assembly. Here is a picture of the new one I just got (picture stolen from pjmoreland's thread):



Here is a picture of the one I took out of my truck (ignore the red parts, they were put there when I was looking for a new top lever):



As you can see from the top picture, there are three vacuum hose connections on the new one, as opposed to my assembly, which has two connections. Can anybody tell me why? Should I just take that part off of my old assembly and use it on the new one? Where does that other hose go? I'm pretty sure that the line controls the fresh air vent vacuum pod, but I don't know what the third mystery line is for.

Thanks