Vacuum leak on the W201 will result in full heat out the defroster vents. Pod failure and you could lose enough vacuum when that pod is selected to go to full heat as well. The W201 no heat comes out the center vents, only outside air and AC air. So you would not get heat out the center vents anyhow to match the heat of the outer. But you will get cold since the air never flows over the heater core to get to the center vents. But the AC will still come out them vents. So start looking for a vacuum leak. Since by design when the temp wheel is in the cold position and the AC selected the Aux pump will turn off and the heater valve will close. Maybe your heater valve is where the Vacuum leak is or maybe the vacuum leak is at the vent pod. When you select other vent controls on the CC unit do you get proper air flow at the correct places, in other words are the right flaps opened and closed to match your selection?

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~Jamie
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2003 Pewter C230K SC C1, C4, C5, C7, heated seats, CD Changer, and 6 Speed. ContiExtremes on the C7's.

1986 190E 2.3 Black, Auto, Mods to come soon.....