I have just purchased a 1998 R129 SL2800, and have struck problems with the central locking system.
The car locks from the key- doors, boot and interior lockers.
However, the car will not unlock remotely from the key. I can unlock the drivers door with the key manually, but all other locking devices will not activate- indoor lockers, fuel flap and boot.

The pump unit was replaced 14 months ago by the previous owner.
Before I buy a new unit, is there any advice members might be able to give on checking systems? It seems odd the locks work one way ( pressure or vacuum?) but not the other.

thanks

 

it's not too unlikely that a new pump could be bad. was the old one replaced with used or new? check lines to the pump in the trunk

 

Thanks
The original pump was replaced by a 'reconditioned' pump and apparently worked OK for 14 months- until I purchased the car.
I haven't costed a new pump yet. Replacing it with a new one is a sure way of finding out if this is where the problem lies. Expensive if not.
I have seen a video where the vacuum lines are tested for pressure and suction, but unfortunately I have not been able to find the link again.