W202 Climate Control Issues

[elegance4]

I have a 1995 W202 with the first generation push button unit. Everything works fine but no air comes out of the center vent when accelerating. When this happens, I can still redirect air flow to the footwell and defrost. I replaced the vacuum control unit under the glovebox as it squeaks when the AC is off, but that did not solve the problem. Upon checking under the dash, I saw two vacuum tubes connected to the center vent flap via a "T" connector, one connected to the vacuum control unit (solenoid) and the other one routed behind the passenger's airbag. Disconnecting the the second tube (routed behind the passenger's airbag) and sealing one side of the " T" connector cured half of the problem. Center vent is no longer shutting off when accelerating, but the air flow is not as strong as it was before. I believe that the second vacuum tube should assist in openning the center flaps. Can someone tell me where the second tube is routed to ? the vacuum tank maybe ? if so, how can I access the tank ? or could it be the manifold under the hood on the passenger side that is cracked (although not evident)? Is there a check valve that I should look at ? Anyone with experience in resolving this type of issues ? Any help would be greatly appreciated. Thanks in advance.

Willy