Wierd A/C vent Operation after Repairs
 

Thanks to the many threads on here about this topic, I recently changed two vaccum actuators in the dash of my 85 300SD which I found to be leaking vaccum and keeping the defroster on all the time and not allowing air to flow through the center vents. After replacing these actuators, I also found that the vaccum that was leaking through those diaphrams were also causing my engine to keep running after I moved the key to the off position (yet another insight from other threads), so I guess everything is not all that bad!

The problem is the following: Now, after I went through the body contortoning difficulty of changing these actuators, it seems that when I drive the car and it is actually moving, the air is still being directed to the defroster, while allowing some air to come through the center vents. When I come to a complete stop, the defroster flap seems to close and the full air blast (the way I like it) comes through the center vent with NO air going to the defroster (the way it should be).

What is that? Do I have a gremlin living in my duct work or what?? Please help! Could this be a faulty vaccum check valve? If so, where is it?