Would someone please pull off the rubber hose from the door lock air pump in the trunk, put some spit or liquid soap on the hole in the nipple, and turn on the pump. I need to know the proper operation. Does it just barely pump a limited bit of air out (which is what is now happening to mine) or does it create a vacuum and pull in the liquid? Thanks. 81 300SD problem.

Depends on the function... it should make vacuum for lock and pressure for unlock.

-Jason

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

Interesting. So when I lock the driver's side door and the pump starts working, it should provide vacuum? Should this be fairly strong and noticeable because I am not seeing much happen?

With the pump apart and moving the diaphragm back and forth, I get air pumped out of the diaphragm area and through the small red rubber O ring. So I know there is not a problem there. From here it is supposed to go through a flat circular plastic piece which includes the nipple; this piece has a rubber almost-peace symbol O ring and several holes which divert the air - finally exiting via the nipple to the locks. But when I put it back together and plug it back up, I get a pitiful single air bubble and about nothing else from the nipple.

I think I must have messed it up when I took it apart last week and wonder if I left something out when I put it back together. At first I forgot the very small red rubber O ring but figured that out but I wonder if anything else fell out on the floor. I am trying to find a detailed blow up of the air pump to show all the parts but have had no success yet. (As you can see I like to repair rather than replace if at all possible.) Any idea where to find it? I have received a link with the Mercedes manual - looking for a blow up there - but cannot get it to work. Struggling with that while I am supposed to have someone sending a paper manual in the mail; he sent it to the wrong address (my mistake) and it seems to be lost in the mail.

Anyway - thanks for your help.

Adrain