Central Locking - How exactly does it work?

[Stevie A]

Can some expert please explain how the vacuum central locking system works?

Does the vacuum / pressure of the central pump pull all the locks / strikers down / up when locking / opening. ie is it just air that works the locks? Or does the vacuum / pressure just switch each individual lock? Is there any electrical juice going to the locks (190E)?

My two rear passenger doors always open but the strikers stick up about 80% of the time when locking, so I lock them myself manually. Would new striker parts / oil help? The other thing I thought was a faulty valve / switch in the main pump so when locking it doesn't pull enough sometimes to pull the rear strikers down?

 

[andy_k]

you should find a vacuum pump under your back seat (I'm not 100% sure on the location on the 190 but any haynes manual should tell you).

The doors lock entirely on vacuum, the only electrical signal goes to the pump.

If you've got doors that are not locking or opening properly there's a good chance the vacuum seals on the door locks are worn. The seals cost pennies to replace but you do have to remove the door cards to get at them. Less likely is that one of the pipes are split but with the system stripped down you can check the pipes with anything that creates a bit of suction.

HTH

Andy

 

[Zanimat]

....might be worth pointing out that if locking is achieved by vacuum, unlocking is by pressure....or vice-versa..

 

[turnipsock]

There are some wires that go to the door locks. They trigger the pump to run for a short time to activate the locks.

On the pump you should find a conector that has three wires. The wires come from the two front locks and the boot lock.

When you turn the key in a lock, that 'wire' is then connected to 12V or ground (depending which way you turn the key) this starts the pump timing sequence and either locks or opens the doors.

(I hope that makes sense)

 

[syd harris]

I Have merc slk 1996 Central locking has stopped working, any ideas. I fitted new battery to the car last night. Now central locking does not work either with the fob or the key?

 

[television]

Syd follow the sync locking instructions in your hand book.

Malcolm

 

[anyweb]

on my (now sold) 190d, i had a problem with one of the doors not locking,

turned out it was because the door knob was getting stuck due to the door panels having become warped, so it couldnt glide up/down properly,

removal of the door panel and a bit of sticky tape solved the problem

maybe your issue is something similar, the door panels are made of cardboard overlaid with plastic and they tend to warp over time (right beside the window area and co-incidently the door knob) especially on the older 190's

in addition, you may be missing the 'groove' black round rubber that the little knob should sit in, if its not there, you'll also have problems opening/closing

i have a few to spare if you need em,

cheers
anyweb

 

[Hibbo]

....might be worth pointing out that if locking is achieved by vacuum, unlocking is by pressure....or vice-versa..

That is not the case on my 300D - there are two pipes to each lock, and they are locked & unlocked by vacuum - not pressure. Everything is done by vacuum, there should never be any positive pressure in the system. The vacuum pump cannot produce pressure, and on older Mercs the vacuum was simply supplied from the intake manifold.

I would assume the 190 is the same. Merc were vacuum mad.

 

[turnipsock]

There will be a central locking pump somewhere. This should have a 12V supply to it constantly. I'm guessing this is where the fault is as a fuse may have blown when you were swapping the battery.

It's a good place to start anyway.

 

[eric242340]

The central locking pump has a fault memory, and when the battery is disconnected, the pump needs to be reset. as do your keys. simply take out the pump fuse for approx 60 secs and it clears the fault codes itself. also the central locking only works on vacuum and not pressure. by disconecting individual pipes on the pump and applying vacuum, you can check for air leaks.this situation also applies to the door assist pumps where fitted.

 

[OmniCognateNeutronRangler]

Central Locking - How exactly does it work?

Occasionally......in my case

 

[syd harris]

Central locking

Tried removeing fuse for 60 seconds, central locking still does not work. The alarm is going off about every hour and the battery has went flat again. Have charged it again and checked it seems OK. Refitted will see what happens. Do you know where the vacuum pump is on an SLK?

 

[turnipsock]

Is something draining the battery?