My 190D is blowing A/C cold air from center vent but hot air from 2 side vents and defrost vent. It is a common problem and could be caused by the heater valve, vacuum or climate control unit. Anyone knows the default position of heater valve? What is the position of the valve when there is no vacuum - hot water passing thru or blocked?

No vacuum can be caused by leak, faulty diaphragm, CCU faulty, or switching vacuum solenoid. Answering the question will give me some idea on how to proceed. Thanks.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

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1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.