1995 W140 PSE Vacuum Pump Questions

I have a 1995 W140 S420 with a bad central locking pump (PSE pump), or at least I think I do.
Symptoms... 1) Everything using vacuum off that pump is dead...door lock, trunk latch,
fuel filler door, etc. 2) HVAC vents seem to go into "fail safe" mode upon acceleration - I've read where this pump provides extra vacuum for the HVAC system when needed. 3) With rear seat and protective foam box removed, I can hear what sounds like a relay actuating in the pump...a "solid" click, whenever I think the pump should be turning on and off. I do not hear or feel the motor run, like I can with the closing assist pump under the same circumstances. 4) Just to be thorough, I checked and get no vacuum on any line from the pump at any time. 5) Yes...I checked the fuses.
Questions... 1) How can I do a bit more incisive debugging ? I can't make sense of what alldata.com has. I would at least like to check supply voltage and a control signal or something. Anybody know the pinout on the pump? 2) Assuming I have to buy a new one, I checked and found it offered on at least 8 different websites. I found a high of $569.20, 5 at $485.6, 2 others in the $400's, and one at $292.00! My unit matches both the Bosch and MB parts numbers of all the websites. I'd obviously like the one at $292.00 but I'm wondering what I'm missing if everyone else wants 200 bucks more. The site is www.autohausaz.com. Anyone have any opinions on them? I haven't seen anything on any of the sites (remanufactured vs. new, etc.) that seems to explain the big difference. 3) I seem to remember one site mentioning that a replacement pump may have to be reset by the dealer. Anyone know anything about this?
Notes... I took the pump out in order to try to play with it and maybe rebuild it (a la the duovalve rebuild of Pete at http://v12uberalles.com/Rear_AC_System.htm ...that saved me $500...thanks Pete). However, I discovered the car will not start unless the pump is hooked up. I got lazy and pissed and just hooked the whole thing back up and didn't bother to check what part of the hook up controlled that.
Anyway...thanks in advance for any help...John
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John Martuch wrote:

Have a look at an image I took of mine as opened;
http://www.pvv.org/~syljua/merc/PSE_Internals_large.jpg
If you dare, and I think you must, since it sounds like a internal fault, I would open it and connect the harness to see where the fault can be. Seems there is a relay in the middle of the board. If the motor does not run at all, you could try to feed 12V directly to it and see whats happening.
If the motor does not run, I have seen people exchange that with a motor from a VW pump (Corrado?).

I have stated that for the lumbar support to work after a timeout, that circuit has to be re-enabled at the dealer. I think that is just related to that function.
br, syljua
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Syljua...Thanks for the feedback. Once I found out the car wouldn't start with the pump disconnected, I didn't have the courage to open it up for fear that I might disturb whatever inside the module enables the car starting. I will follow your recommendation on direct voltage to the motor and see what I get. I'd love to be able to solve the problem with a pump motor from VW.
Thanks again...John
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The site is www.autohausaz.com. Anyone have any opinions on them ____________________________________________ "I have made serveral purchases from them....A/C climate control unit, window switches, etc, and found that the merchandise is top quality and their service is excellent.
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