This group provides a forum for owners and operators of diesel powered motorhomes and 5th wheel tractors to discuss mechanical issues, regulatory issues (US, Canada), ownership, insurance, campground accommodations, trip reports/suggestions, and other topics relevant to large RVs and the people who drive them.
Two trouble shooting guides.
http://dieselgiant.com/mercedesvacuumtroubleshooting.htm
https://www.ifixit.com/Guide/Mercedes+W123+Vacuum+Lock+System+Diagnosis+Technique/20201
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Stan George Portland <<
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Nate sent this a few years ago. I believe it's by Tony Clark. It
helped me sort my vacuum line issues.
> The trunk automatically locks with the doors and fuel filler door.
> It should unlock with them too.
> Because your doors are not unlocking, your trunk and filler door
> remain locked (like the other 3 doors do).
> You need to identify the actuator or hose which is leaking.
>
> * Does the Vacuum assisted braking operate normally? No -
> it could be a vacuum pump issue.
> * Do the doors unlock with the engine running, but not when
> stopped? Yes - Indicates a leak in the unlock circuit
> * Do they lock with the engine running, but not when stopped? Yes
> - Indicates a leak in the lock circuit
> * How long after the engine is stopped do they stop working? Long
> time indicates a small leak short time indicates a serious leak.
>
> Your symptom that the doors and trunk do not unlock indicates that you
> need to start work on the unlock side. Under the drivers front
> carpet, there are a couple of rubber Tees connecting the vacuum lines
> for the central locking. Identify the unlock Tee by having the
> drivers door unlocked with the engine running and checking for vacuum
> on the vacuum line coming from the A pillar to each Tee. Vacuum
> should only be present on the unlock side. If vacuum is not present
> on the unlock side, check on the lock side. If no cvacuum on either,
> check the vacuum hose under the hood, as one or more may have come off
> the rubber "octopus" near the firewall.
> If you have unlock vacuum there, block off the vacuum hose going to
> the firewall using a Golf Tee. The drivers side back door should
> unlock and lock with the engine running.
> Repeat this for the rubber X on the passenger side floor to check the
> front door operation, blocking off the port going to the rear of the
> car. IF both sides work OK, the problem is in the Fuel door or trunk
> actuators. The door key should fit the trunk. This may be different
> to the ignition key if the ignition lock has been replaced at some time.
> This is easy to diagnose, but takes time. Mechanics generally cost
> much more per hour than I can afford, so I prefer to do the easy, time
> consuming stuff myself.
> I hope this helps,
>
> Just remember : the vauum pipes for the central locking are yellow ,
> green tracer means unlock circuit , red tracer means lock circuit and
> brown tracer is for the reserve tank in the trunk ~ .
>
> Don't forget to test the one way vacuum valves at low vacuum as
> they'll show the leak faster with 1" of vacuum than they will @ 20" .
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Stan George Portland <<
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I'd check the door lock actuators with a vacuum tester, the lagging one 1st. You can check them by finding the vacuum lines under the floor matt, or tear apart the door. The rubber connections can also leak, as well as the gas door lock and trunk.
Rob
GG
On 11/17/15 3:53 AM, Lawrence Rhodes primobassoon@sbcglobal.net
[diesel_mercedes] wrote:
> My door locks seem to be fixed by the rain we have been having lately. What part of the vacuum system is affected by humidity. I'm voting for the door lock actuators. One of them is always lagging and when working I only get about two or three openings and closings. Lawrence Rhodes
>
>
> ------------------------------------
> Posted by: Lawrence Rhodes <primobassoon@sbcglobal.net>
> ------------------------------------
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>
> Yahoo Groups Links
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>
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My door locks seem to be fixed by the rain we have been having lately. What part of the vacuum system is affected by humidity. I'm voting for the door lock actuators. One of them is always lagging and when working I only get about two or three openings and closings. Lawrence Rhodes
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