Friends -

I am working on air distribution for my A/C for my '87 300TDT and am replacing some of the vacuum pods, but in doing so I gauged the amount of vacuum coming into the 7 port switchover valve behind the glove box, and I don't have enough vacuum coming in there to fully actuate anything.

The first pod I was replacing was the one behind the glove box that controls the defrost flaps up to the windshield, and I need 13" of Hg to fully close that flap - but I am getting maybe 7" on the gauge. This means even the pods that are not damaged won't move all the way to open or closed. I did gauge this off the 7 port manifold - so the leak is further up line.

There is a green/yellow line that by the diagram heads back to check valve, and then a grey line that connects to the intake manifold.

Where is that connection in the engine compartment? I am not finding it, and would like to work upstream to fix my vacuum leak.

Also, I did recently disconnect and cap the vacuum lines to the EGR valve and recirculating air valve, and was going to remove all of the transducers, but there is a larger diameter black vacuum line that connects into a filter connected to the tranducers that is labeled in the diagram "ventilation to passenger compartment" and I wanted to know where that is going and what it does so I understand how to remove things I no longer need to preserve my vacuum pressure.

Here is the link to the diagram I was referencing for the engine side vacuum
http://i323.photobucket.com/albums/nn447/Jeremy5848/1987%20Mercedes%20300D/Vacuum603.jpg

The diagrams I was referencing for the A/C side were from the cd shop manual for the 124 series.

Thanks for any help!

__________________
Jimmy M.

87 300TD 230k mi's

Per your diagram, follow the line marked 'c' from the engine vacuum pump to the cabin. IIRC there's a check valve near the firewall before the line goes into the cabin. once inside the cabin, the line splits to the ACC solenoid bank and rear headrest release mechanism. I don't know if there's a check valve between the two system. If your headrest release feature doesn't work, you might have found your problem.

Gray line to the intake manifold? There's no vacuum in the intake manifold of that vintage of MB Diesel. The only line from the manifold goes through the overboost switchover valve then to the ALDA and BFS. That line never makes it to the cabin unless someone tapped it for a boost gauge. Or the diagram with a gray line is for a gasser 124.

Don't worry about the big black lines. They're just vents for the vacuum actuators. You can leave them or remove them.

Sixto
87 300D

Sixto - Thanks for the response!

I was wondering if 'c' was it, but a little hesitant to test my vacuum strength right there at that 5 way split off the vacuum pump. So it sounds like I can remove everything to the EGR and recirc valve including the larger diameter black vent line.

I don't completely understand about the headrest "release" mechanism. I have auto seats and headrests for the front seats, and those seem to work fine. How does vacuum connect in to that - or am I misunderstanding?

What is the ACC solenoid bank? Is that the 7 port manifold, or something prior under the dash? I am planning to replace all my vacuum pods under the dash, as several are shot, so if it is there I can check it out then.

Additionally - shouldn't the system hold vacuum after the engine turns off? When I was testing the connection from the engine to the 7 port manifold it had no vacuum till the engine was up, which figures sense I had opened the system to connect the gauge, but then right after I shut off the engine the vacuum dropped immediately, which I am thinking definitely means a leak - because if it is sealed it should hold vacuum for a while if not indefinitely. Is that correct?

__________________
Jimmy M.

87 300TD 230k mi's

Oops, TDs don't have a rear headrest vacuum system. Hmm... you can trace the vacuum lines from the 5-way connector over the engine vacuum pump. Two go over the radiator to the passenger side. You can disconnect those lines and cap the branches of the 5-way connector if emission control is not a concern. Of the remaining downstream branches, one goes to the transmission vacuum control valve (VCV) and the other goes to the cabin for ACC. You can follow the lines to the bulkhead grommet by the brake booster. I don't know where there are natural breaks to test. If you see low vacuum rather than no vacuum, you might be looking for a stiff and disintegrating rubber connector.

I don't know how long the ACC line holds vacuum. It might be that the system vents when power is cut to the solenoid bank.

Sixto
87 300D