I've been trying to figure out why my vacuum pump in the trunk keeps kicking on and off. I found a vacuum hose under the hood. It run across the firewall from the compartment that has all of the vacuum lines in it across to the brake reservoir area. It's a white line that has a black rubber 90 degree coupling on it. The coupling was stuck on the end of a screw! Can someone tell me where this line should connect? I've looked in the area where the brake fluid is, but can't find any open connections.
Thanks

 

As far as i know, the vac pump in the trunk is for door lock/unlock. If it keeps charging noticeably, logic suggests that either the pump gets too old or somewhere along the line, there's a leak.

 

I know - I was just checking under the hood. I've already checked from the trunk up to the engine compartment - I just ran across this line while I was looking and was hoping someone could tell me where it connects. I don't think Mercedes would have put a line in the engine compartment just to plug it onto the end of a screw

 

According to what model it is, for example on my 450SLC the vacuum line goes back on the driver side and then across the back and the in the front of the trunk it turns to the right side and there is a rubber splitter that send vacuum to the gas cover door and the other line goes back and over the trunk lock. There is no vacuum pump there are several check valves in route and a vacuum element near the lock to pull and push the handle to lock and unlock. Let me clarify, if you have a gasoline engine there is no vacuum pump. Vacuum for the car is drawn from the intake manifold. There is a vacuum storage tank also. But the brakes locks and ACC on my 450SLC come directly off the intake manifold, and they split into the other systems from there. Diesels have pumps as they ar a poor source of vacuum. There are two possibilities. one if the line under the hood connected to a splitter and the splitter was caught on a screw replace the splitter. Next if there is a check valve before the splitter check to see if it is holding vacuum. These little devices are stop gaps, if there is a vacuum failure the check valve closes so vacuum is maintained. There should be two black and blue or all black. if these check out, then check the connection at the element by the lock. it could be the pull rod is worn. Or as in my case my trunk doesn't lock or unlock centrally, as the lock is shot. The vacuum to it is fine, but the pull mechanism is worm out from age.

 

you need vacuum diagram...?

 

YES - that would be great! Thanks. This loose line is driving me crazy! I know it's supposed to be connected to SOMETHING.

 

the tell me the VIN

 

VIN WDBHA28E2SF196744

Thank so much

 

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Thanks for the diagram....that will help with my rear headrest problem. I still need one for the vacuum lines in the engine compartment. Anyone have one? I've got two lines running across the engine firewall: a green and a white. The green one curves down and looks as though it runs to the transmission. The while one is just hanging in the compartment with the brake fluid reservoir.