Steve,
There is a vacuum terminal of sorts behind the climate control unit on the center console that services all the major vacuum lines. I'm not sure if it's easier to get at by removing the ACC or by removing the passenger side kick panel, it's been quite a while since I've done it. Maybe someone else here has done it recently and can offer more specific help. Once you get at it you'll want to remove the lines one by one and test them with a MityVac to see which line operates which actuator. You should be able to hear them open and close (with the engine off obviously). Switch the line for the center vent with the one that operates the side vents. You may need to experiment a bit to get it right. Take some notes so you can put things back as they were in case you need to. Good luck.
LRG

__________________
LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold