83 300SD Door Locking Vacumn Pump Problem
 

I have avoided chasing door locking problems since I got this car several months ago.

I started in the trunk by checking the pump and it seemed to have a loose electrical connection after addressing that and getting the pump to run I had the vacumn line disconnected and found the pump pumping air OUT not a vacumn as I expected.

As a vacumn pump this does not seem right. Is it wired backwards? Or what.

:(

Any suggestions would be appreciated

Answer
 

the vacuum pump exhaust is air pressure.

It generates vacuum in the central locking system. :)









Have a great day.

Testing the pump
 

Before I sell the vacuum pumps, I test them with a 12 volt source. In my case I use a battery charger.
I apply the negative cable to the brown wire of the pump. Ground.
Applying the positive to one of the other wires will make the pump push air or suck air. Depending on which wire I started with.
The pumps I work with are the ones with the three wire pig tail. The newer ones have a second connection.
I don't get into those yet.

Looking closely at the pig tail you will notice it's shape. There is a flat surface on the round male plug. In order not to plug the pump in incorrectly, the male plug inserts so the flat part contacts it's mate within the female part.

I can not confirm if the pump it always suppose to "suck" air when connected correctly. But if you can match up the color of the wires from the car with the pig tail your task is done.

I just went got done working on my lock system (83 SD), i found that I have a bad chip in the circuit board. The pump will create a vacuum to lock the doors and create pressure to unlock.

If the pump is working when you unlock and lock the drivers door then you probably have a vacuum leak in the yellow line. The line runs down the passenger side under the carpet. There is a connector that splits the system by the passenger seat, you can start here and isolate half the system by disconnecting the T and checking for vacuum. If you have no vac. then the problem is between there and the trunk. Good vacuum tells you that the problem is from there forward.

On the 3 wire conector the brown wire is ground and the blue wire controlled the lock and yellow the unlock.

If the pump doesn't seem to be running if you when you lock or unlock the drivers door check to see if you have power at the pump with a test light. Hook the test light up to the brown and the yellow or blue, then lock and unlock the drivers door the test light should come on in one of the positions. Then test the brown and the other wire, The light should come on in the opposite postion as the last test.

If nothing happens no pump or light remove the driver side door panel and check the lock accuator, it is mounted with 2 8mm screws to the inside of the door. (follow the door lock pull) There is a 3 wire connector here (yellow, blue and black/red) check for power with your test light at the R/B wire, this should have power all the time. The yellow and blue wire good directly to the pump.

If you have power try jumping the R/B wire to the yellow and blue wire one at a time. If the pump runs the accuator may need to be cleaned.
If the pump dosen't run the wires may be broken, they usually break where the door hinges.


Hope this helps

Look at post #13 of this thread. I have and 83SD and this is the system as I have found it.
http://www.peachparts.com/shopforum/diesel-discussion/150356-door-locks-1982-300sd-w126.html

The pump is a combination vacuum pump/compressor. It creates vacuum to lock & pressure to unlock. It makes sense it would be creating pressure since the door locks are most likely in the unlock position. If you plug the pump output while it's running it will actuate a shuttle valve & switch mechanism inside the pump which will shut off the pump & prepare it for the opposite function (lock) once the desired pressure has been obtained. If the pump is allowed to run without achieving the desired vacuum or pressure a timer circuit within the pump will shut it down after about 20-30 seconds. You must disconnect the power to the pump once this happens to reset it.