PeachParts Mercedes-Benz Forum - View Single Post - 79 450sl- No Heat!!!

Richard Wooldridge · #17 12-02-2006, 09:23 PM

Hi there,
As I stated in my previous post, the blower operation is NOT dependent on the servo for it's on/off function, the MAIN vacuum sw. #19 is responsible for turning on the blower in all positions except the defrost position, and if you don't have enough vacuum to operate sw 19, it just "aint gonna work, no way, nohow." Please reread my previous post carefully and check the items I listed for your fix. The servo IS responsible for the blower SPEED control as well as modulating the heat in the normal operating mode. Note that vacuum switch #35, a bimetallic switch on the bottom of the servo, is monitoring the engine temperature, and won't let vacuum sw 19 "make" until the engine water temperature is at or above 104 degrees, which with a good vacuum system will cause the blower to then turn on. You can bypass switch 35 by connecting those two vacuum lines that go under the servo together, but you will loose the delayed blower on feature.
With the ignition turned off, you should have +12 volts at pin six of the amplifier, which should cause the servo motor to park in the P position. If you don't have it, fuse 12 is blown. It's in a barrel container, not on the main fuse panel.
I do have the factory manual for this climate control system, and the info I'm giving you is straight from the manual...