Mercedes-Benz W123 vacuum central locking not working
Why does the W123 central locking not work or not hold pressure?
The W123 central locking runs on vacuum, so an electrical fault does not usually explain it. The cause is almost always a leak in a vacuum hose, in the door pressure capsules or in the branch fittings. If the vacuum is lost while the car is standing, the other doors only unlock once the engine is running.
Which part of the central locking usually leaks?
The most common faults are a hardened collar seal on the door pressure capsule and a ruptured rubber diaphragm in the capsule. In the vacuum cylinder, the rubber boot where the rod passes through cracks over time, and the leak then shows only while the doors are locked. A hose that has come loose in the engine bay can also be the cause.
How do you check a vacuum cylinder for a leak?
Connect a short piece of hose to the cylinder's fitting and suck on it: the leak can be heard and seen from the movement of the piston. You can also block two openings with your finger and press the piston down slightly. If the piston does not go down, the rubber is sealed. The door pressure capsule can be tested by blowing into the hose hole.
How do you find where the leak is in the system?
Check the hoses from end to end and make sure they have not been connected the wrong way round. If the leak is in the driver's door, the whole system works slowly. A leak in a rear door shows only as that door opening slowly. The vacuum reservoir is under the rear parcel shelf on the boot side.