From the top (at least on my 300SD) Best I could figure from the car and the CD.
1. defrost flap valve
2. footwell flap
3. center flap
4. diverter flap
5. fresh air/recirculating flap
6. fresh air/in car flap
Test each with you MightyVac and you'll probably find a bad vacuum pod.
The Golden Rule
1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)