The vacuum to the heater valve is either on or off. Blending is done with the blend air doors that the "feedback" potentiometer sits on. The pushbutton allows variable vacuum to the element for feedback thru the switch-over valve assembly. NOT a simple system!!

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MERCEDES Benz Master Guild Technician (6 TIMES)
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190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
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