I have been trying to solve a climate control problem, hot air through side vents in all modes of climate control operation. I have examined the operation of the heater control valve. It appears that the vacumm servo is good as the valve closes when the a/c is switched on and holds vacuum when tested with a vacuum pump. But the hose on the passenger compartment still gets warm. I purchased a new valve but did not install it because I tested the new valve by hooking it up to the vacuum line on the car and it does not close all the way. Approximately how much vacuum must be present at the valve? There is about 3.5 inches reaching the heater control valve. Is this enough?
Thanks.

The reason is usually the blend flaps not operating in range. There is a potentiometer on top that sends a signal. It has to be perfect. You will need the CD or take it to a shop.

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Benzmac:
Donnie Drummonds
300E
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM