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johnr_03 12-24-2009 12:05 PM

Heater vacuum system
Hello from the UK,

I am new to the forum and this is my first post. In May 2009 I rescued a MB 1972 350sl from a's a long story!!!

Its up and running well now but as the winter has arrived I found the heater doesn't work.

The problem seems to be the vacuum system that activates the heater valve that allows the hot engine water to flow into the heater box. If you look at the picture you will see a black pipe with a blue check valve...can anyone tell me where that connects it on the manifold or, some where else?

Bear in mind that this car is the European early model and has just the basic heater and no Air Con.

RadioTek 12-26-2009 12:36 AM

I was going to upload the .PDF of the pertinent section of the service manual, but it's 5 KB too big. :mad:

From the photo, it looks like the hose you are asking about goes to another "Y" connector. One side goes to a manifold vacuum port, and the other goes to the vacuum reservoir. If you were to PM me with your e-mail address, I should be able to send you the file.

Best of luck,

johnr_03 12-26-2009 06:34 AM

Thank you for your help Scott but I had a message from Barri who knew the answer and this is it.
The pipe actually fits to a spigot (I thought it would go on a "Y" branch) which is at the rear of the manifold on the left hand side facing the car and it points to the back of the car. The only way you can see it is with a mirror. I have take a picture of the spigot but remember it is through the mirror.
Once I had found the connection I then had to clean it off and re-connect the vacuum which was a job in its self.
This was good example of poor MB design.

Many thanks to Barri and Scott.

Regards, John

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