The Audi 5000S used a bi-pressure pump mounted in the trunk.
The door switch reversed the polarity of the pump so it would pressurize to open the locks or vacumn to close the locks.

You could use that for you seats pmckechnie





.

At least some models had the pump under the back seat, IIRC.

Going all electric and getting rid of vacuum in the Mercedes is quite an ordeal.

Here is a list of all the vacuum elements in your 300CD.

Lock system:
Drivers door control valve.
Passenger door element.
Seat back control elements.
Fuel filler door element
Trunk element
Vacuum reservoir
All lines and connections

AC elements:
Floor heat element
Defrost element
Fresh air element
recirculation element
Center vent elements
All your air valve control switches

Engine vacuum controls
Vacuum pump
Brake booster
Engine shutoff
Transmission shift control
EGR control
ALDA input

So to eliminate all the vacuum would require redesigning the AC control, engine control and transmission control????

Do you really want to take on those problems??

It is easiest in the long run to maintain the system as designed by Mercedes, And less frustrating.

To change your car to a manual AC system you need a manual donor car and all its parts. Then you still have to figure out how to attach the wire harness to the manual system.

Dave

IIRC the pre '82's where in the trunk but they got wet...later where under the rear seat on left side in a foam housing.




.

Great list, thanks.
EGR? What's that? :brows:
The ALDA input is boost referenced.

I agree, chances are the conversion is not worthwhile. But you never know 'til you ask. For example, think if the a/c system could easily be converted to manual control, like a simple swap with a 240D. I bet about half of us, the half with persistant vacuum leaks, would have done it.

boycott?
 

as much of a PITA as it is to troubleshoot the vacuum system it is uniquely cool..
akin to the love of diesel power that we are drawn to in the first place.:D

I do have to admit that seeing the passenger lock sweeping closed gracefully is cool... much better than the electrics click!
Speaking of which, does everyone elses gas cap lid kinda thunk as it locks?

I got a a used pump from a fellow forum member for $40 shipped, including connector. It looks brand new, and works like new.

my w126 needed it.

Would not exactly call it easy. If you had a 240D and your "modern" car sitting next to each other, think about the job.

Remove both center consoles. Which means removing both drivers seats.
Remove both dashes
Recover the freon from both AC systems
Remove all controls, keeping track of all controls and their conections
Remove both evaporator boxes.
Replace the evaporator in the 240D box that is going into the "modern" car ( all that work and not replacing the evap would be foolish)
Installing the 240D evap box into the "modern" car
Install the 240D dash into the "modern" car ( center air vents and air temp sensor design difference, hopefully the same color)
Install the center console. Either the 240D console or put the 240D switch panels in the "modern" cars center console. AC switches are different
Figure out the wiring.
Replace the mono valve and tubing with the 240D heat control valve in the engine compartment.
Remove the water circulation pump to the ACC system.
Connect everything and make sure it works.
Charge the AC system and hope you don't have any leaks.
And after all of that the 240D still uses a vacuum element for recirculated air.

It is possible but after removing a 300TD AND a 240D evaporator box to replace the leaking evaporators, I find it easier to just keep the systems going as designed.
If you wonder what it looks like.

http://www.peachparts.com/Wikka/W123Evaporator

Dave

So the topic should change to "How can we help you with your vacuum leak problems???"

I would rather work on a vacuum problem than swaping a AC system.

I meant if it were an easy, simple job a lot of us would have done it. I was aiming more at the preference for simple, reliable parts than whether the swap itself was difficult or not. Any time you start talking about removing a dash I'll give you the Major PITA factor without question.

I wouldn't do it, I'd rather troubleshoot vacuum systems than electrical systems any-day. Once you get everything working correctly, it's pretty easy to fix individual problems as they come up.

I don't see how it would be all that difficult to swap the HVAC system from a 300D to a 240D. I have had the dash out of my 300D twice, once to replace the vacuum solenoids and the other time to replace the heater core. To do the heater core the whole HVAC box had to come out. Time consuming and tedious, yes. Difficult, not too bad. If I had a 240D sitting in the next garage bay to swap the parts directly over it would be pretty simple.

Granted this is pretty involved and you have to have the tools, space, parts car, time and ability to pull it off. Its a lot of effort but the result is a much simpler HVAC system and likely years of trouble free operation. I came very close to doing just this when I had to go in the second time to do the heater core. I just couldn't find a 240 donor fast enough. RT

Hi , please unerstand electric or vacuum the princeables are the same ! just remember its all about flow ! think about it, all you have to do is get a schematic and isolate the circuts !! whats the differance between a
vac-pod or a solinoid ? a diode or checkvalve ? wire or a hose !!to me its the same! For the amount of time to convert I could rebuild a 617 !my 2 cents !:confused: :confused:

Are you talking about the vacuum pump that sits in the spare wheel well? I have a working one from a diesel W126. Pm me if you want it ill let it go for cheap.

It's easy to see electrical leaks. Or feel them for that matter.