PeachParts Mercedes-Benz Forum - View Single Post

Richard Wooldridge · #5 05-10-2006, 11:37 AM

Hi again,
Sorry Strife, this one isn't the ignition switch problem. If it were it would fail in the defrost position as well as any of the other positions. Vacuum switch #29 or #30, (going from memory here) is the one that stops the blower from running if the vacuum is low. All the ACII climate control systems behave like this if there's a leak in a vacuum pod. The leaks can be very difficult to find. Another (slight) possibility is that the one way valve that feeds the AC vacuum system is defective, allowing vacuum to go away when the throttle is pressed. Usually the vacuum reservoir will hold the vacuum in a good system, but if the one-way valve is leaking in the reverse direction it could allow vacuum to go away. The vacuum pushbutton control has very small orifices, on the order of .040 or so, so it won't take much of a leak at all in a vacuum diaphragm to cause a failure. Besides the diaphragms, the vacuum switches themselves can leak and cause this failure. The connections to the servo unit can also leak and cause the failure. In short, ANY vacuum leak will cause this failure, the system must be tight.
There is a digital servo upgrade kit available for when your servo fails that is a good investment if you are going to keep the car. Look at the top of the SL forum main window for their advertisement.