I am trying to get the central door locks on my 82SD. Seems like whenever I disconnect and reconnect the battery, the door lock vacuum pump starts up. When this happens, the door locks work fine. I can lock/unlock the doors and each time I do I hear the vacuum pump start up and run for a few seconds. After doing this about 3 times, I get nothing. The vacuum pump does not start, and the door locks do not work. Probably have a vacuum leak, but when the pump starts, I have enough vacuum to unlock/lock the doors.

Can anyone tell me what the normal function the door lock vacuum pump is? Also, is there a relay somewhere that controls it?

Thanks in advance.

__________________
1989 300E
103,500 miles

1982 300SD
Sold but not forgotten

I think you have a bad vacum pod in one of your doors. Check them out and put a golf tee in the hose.

__________________
If it ain't broke take it apart and find out why.

1983 300SD, 4 speed
1994 C280
1987 300TD wagon
1996 HD Road King

Ride in Peace Eric Peterson, Harley of Macon

The electric vacuum pump on the W126 provides positive pressure to unlock, negative pressure (vacuum) to lock. The electric switch in the driver's door lock element activates it. Once activated, it will pump to either + or - 0.5 bar, at which point a lever in the pump switches over to the other side (vacuum or pressure, as the case may be) in preparation for the next operation.

An internal pressure switch senses when +/-0.1 bar is reached, at which point this switch ensures continuous power to the pump until it reaches +/-0.5 bar, regardless whether you turn the driver's door key in the opposite direction while it's operating.

An electronic cutout device turns the pump off after about 45 seconds if, due to a leak, it cannot reach +/-0.5 bar.

There are two styles of electric pump. Most of us have the one mounted in the spare tire well, but some of the earliest cars apparently had one mounted in the engine bay. According to the FSM, they operate the same.

As far as I know, there is no relay, although there should be a fuse (try #13).

If all your locks (including the trunk and fuel filler door) properly open and close for three cycles and then the pump quits, I'm inclined to doubt there's a simple leak. If you leave the car alone for awhile and try again later, does the system work then? If so, maybe the pump motor or the cutoff switch is wearing out, such that a few cycles heats it up to the point where it stops working correctly.

I had the same problem and this was the fix that time
http://www.peachparts.com/shopforum/showthread.php?t=128813

Also later I had a problem of one of the wires breaking at the door hinge of the drivers door so I spliced in a new wire.
If you have to get into the vacumn tubes the are all in a trough under the front passanger side carpet and all are manafolded together in there so you can test each circuit in one lication.

__________________
1983 300SD
200000miles

Phil,
Thanks for the post
" I removed the pump from the trunk and took the cover with the four screws off the back. Inside there is a circuit board with wires attached. I lifted this board away from the chamber that it was mounted in. Underneath I found that the board was connected to two long, small width spade connectors. I cleaned these connectors and bent them slightly for better contact. Also on the board is a small relay. I cleaned all the contacts on this. I then put it all back together. It all works perfectly now."

I have removed the pump, but I can't find the circuit board you refer to. Did you take the pump apart? Also, for what its worth, the last time I plugged and unplugged this pump, I blew my #13 fuse.

__________________
1989 300E
103,500 miles

1982 300SD
Sold but not forgotten

The pump will only cycle a few times after disconnecting/reconnecting power. After that, the pump never comes on again.

__________________
1989 300E
103,500 miles

1982 300SD
Sold but not forgotten

for now at least. Per Phil's advice, I pulled the pump. Mine did not have the 4 screws and printed circuit board though. There were two screws that when removed, revealed three wires running to what I assumed to be the pressure switch. With a magnifying glass, and flashlight I resoldered the connections.

Also inside this housing there was a small white plunger/ switch looking thing. I gently pushed on it with my small screw driver and could feel it clicking back and forth (pressure switch??). I did this several times, thinking that maybe it was sticking.

Reassembled, and the locks have been working now for over a dozen cycles.

Thanks pointing me in the direction of the pump and switch.

__________________
1989 300E
103,500 miles

1982 300SD
Sold but not forgotten