Does anyone by chance have a schematic of the vacuum lines behind the dash for the heater for a 79 450SLC (107)? No heat and it is a wee bit cold.

Thanks. SMW

I can e-mail that diagram....BUT vacuum has nothing to do with heat...But only where the heat comes out.. The servo controls heat!

__________________
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MB DOC. My understanding is that baffles which allow the heat through are controlled by vacuum. The scenario is that my mechanic took the heater control unit out of the dash to see if we could get some of the buttons n the panel working. The only thing working was the defroster button for heat and the high blower for a/c. After he put it back together, I only have cold air blowing out of the defroster vents and, at the beginning of turning on the blower, out of some of the dash vents. During the process, we discovered that the top of the radiator was not getting hot and two of the water lines on the "heating control unit" (if this is the correct name) mounted on the passenger side firewall in the engine compartment were not getting hot. We replaced the water pump and thermostat and now we are back at no heat and only cold air blowing out of the defroster vents. Our current thought is vacuum, but I am open to any assistance.

Thanks. SMW

I'm afraid MB Doc is right on track... $699 for a digital replacement will probably fix you up. Then you can attack the vacuum lines/pods for where the heat comes from.

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RM Smith
1988 560SL

"Where is it again that we are going, and why are we in this handbasket"?

Where is the "servo" and why would it go out simply by removing the control panel in the dash? What is the proper name of the "servo."

Thanks. SMW

look at the advertisement at the top of the SL forum, it shows an advertisement for the Unwired Tools digital servo upgrade. It sounds like your control servo for the heater has gone bad. You can replace it with a rebuilt for several hundred, or get the digital upgrade unit for about $700. The digital upgrade servo is guaranteed for 5 years, and is the way to go if you are going to keep the car. In any event you should go to the unwired tools website and download their vacuum diagrams, which is what you need to check the vacuum connections. Any vacuum leak in that system will kill the heater. The first sign of a vacuum leak is that the blower will only work in the defrost position. Your car has what they call the ACII climate control, and relies on the control unit, that unit under the hood, to change the fan speeds, control vacuum flaps, and control the water valve's on or off position. It usually only lasts a maximum of three years or so.

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Richard Wooldridge
'01 ML320
'82 300D 4.3L V6/T700R4 conversion
'82 380SL, '86 560SL engine/trans. installed
'79 450SL, digital servo update
'75 280C

Thank you all for your assistance. I now understand the issues much better.

smw