82 300SD Vac Lock questions
 

I would like to gain a better understanding of the vacuum lock function on my 82 300SD so that I may trouble shoot its problems which are:

- Locks down, open the driver's door, no locks come up, but... there is a strong vacuum force present holding them down. When you lift up a lock, it slams back down until the vac pump stops running.

- Locks up, lock the driver's door, no locks go down, I reach over to push down the rear driver's door, all the locks go down and are held down by vacuum.

- Locks are up and pushing the rear driver's door down does not get the rest to go down.

I have read conflicting reports as to the vacuum function. I'm told the circuit is completely supplied by the pump in the trunk, and I'm told it's supplied by the engine vac pump like on my old 123. I'd be inclined to believe the trunk scenario as there are no shut off problems.

I'm told there is a manifold under the passenger seat where I can test for diaphram operation.

Here's where I could use some help. I believe I have good vacuum because of the force holding the locks down. I know the pump is working. What I don't know is what tells the locks to go up or down. Is there a valve in the driver's door? Or is there one in the pump assembly? If I locate the manifold, can I determine from there if such valve might be functioning correctly? I guess I could use some in depth understanding of the locking system beyond it's a vacuum system.

Thanks,

Frank.