OK, well I've spent the better half of a day working on my climate control, and I think I've figured it out (at least for my '85 300CD). I went through all the functions of the ACC, along with all of the vacuum elements and how they control each other. I have the spreadsheet made out, I can't really post it here so you could read it, so if you need it, pm me.

I found that the defrost vents are normally open, feet and fronts are normally closed. The recirculation is normally set to recirculate, and the fresh air is normally set to 20% fresh.

In the end, I decided to disconnect the second line to the defrost element (connected to the front vents). Then connected the front vents vacuum line to the foot element.

Like I said before, I don't know if mine was hooked up correctly when I bought it, but I am pretty happy with the setup I have now.

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My Primary Driver - '85 300CD - 4-speed conversion, 2.47 rear, lowered, euro headlights, rebuilding (not restoring so much)

Wife's - '08 Saab Sportcombi Aero

Riding a '03 Yamaha Warrior