I've posted in vain in the following thread but got no answers -- AC Vents... Center vs Side Vents

My 94 C280 is having the hot air from some vents (usually side vents, sometimes foot vent), cold air from others (mainly middle) problem. It has been indicated that this is typically a vacuum issue but sometimes could be a heater valve.

I do not know where to begin on this. Could someone give me a link with diagrams or give me some pointers?

Side issue -- had my crank sensor replaced a couple of weeks ago. Ever since -- the transmission shifts have been VERY harsh. I'm told that likely some vacuum line was disconnected during the repair. The A/C vent issue started soon after that, but not immediately after that. Is it possible that these are related?

Thanks very much in advance of any help you can give.

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1994 C280, dark green metallic
105k miles

1991 190E 2.6, Black
191,500 miles
(sold to another forum member)

2003 Chevy Tahoe LT, Redfire Metallic
105k miles

1989 Mustang GT Cobra Convertible
43k miles