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.

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)