Vacuum motor buzzing a lot

[mike18hc]

Just switching on the ignition and waiting 5 seconds or so makes the vacuum motor in the boot side panel start buzzing. It can do this for 5 seconds or minutes. After starting the car it'll come on when it feels like it and carry on for as long as it likes. Recently the noise has been noticed by rear-seat passengers...so I'd like to sort this out.
I assume there's a leak in a pipe somewhere but how can this be looked for logically? I've looked at diagrams of the vacuum pipe system but can't really understand them!
Is there information on which flaps operate under what conditions?
The only possibly linked background info is that the car's got AC (working poorly), no climate control computer and it's never blown a good volume of air into the car. Even when the AC was working at its best the car would mist up on a damp or chilly day and take several minutes to clear enough to see through all the screen. The dryer was recently replaced when the AC was investigated.
Can anyone help throw some light on this problem before the pump burns out?!

 

[Dec]

What car is it... W124 , W202.
What year is the car.

Describe the remote key fob that you use to lock/unlock the car

For the time being, locate and remove the fuse for the Central Locking Vacuum pump.

Dec

EDIT; Before you remove the vacuum pump fuse, make sure you can open a door or boot (or wherever the vacuum pump is located) with the metal key blade.

 

[mike18hc]

Buzzing vacuum relay car details

Sorry for the omission.
The car's a 1995 W202 C220 petrol Elegance with a flip-out key for the boot.

 

[Dec]

Check that the carpet in the passenger foot well area is not damp, you will need to lift the carpet to check properly. Windscreen drainage hole can some times become blocked and allow water inside the cabin.
I only mention this because of what you say in your first post… “Even when the AC was working at its best the car would mist up on a damp or chilly day and take several minutes to clear”

[YOUTUBE HD]C_LeuzB36dQ[/YOUTUBE HD]

If you can, check the time it takes to lock and unlock;
=When you lock the car, with the remote, do all the door pins drop down within one second?
=When you unlock the car, with he remote, do all the door pins rise up within one second?

=When you lock the car, with the remote, does the fuel flap locking (Green in picture below) pin shoot out within about 1 second… leave the flap open when you are locking/unlocking so you can see if the pin is working.

The boot should also lock/unlock within 1 second… you can’t see this event happen so you will need to test to see if you can or cant open the boot lid immediately after you lock/unlock the car.


Ideally, when you lock or unlock the car, the vacuum pump should run for about 2 to 4 seconds.
You should check the electrical connectors on the vacuum pump to see that the are clean and open the vacuum pump to inspect its PCB, it does sound like it might be a problem with the electronics inside the vacuum pump unit, below, is yours the same as the one in picture with just one Yellow tube?

Dec

 

[mike18hc]

Vacuum pump/ water leaks checked out

Sorry about the long delay in responding to your help...the weather's not been too good for testing.
The floor coverings are all dry, as is the pan itself, and it still take 10 minutes to clear the screen! The reason I mentioned this originally was a suspicion that the flap controlling the air to the screen might not be allowing much flow, and that might be caused by a leak in the vacuum pipework.
The pump details look just like the ones you posted. The pcb passes the sniff test and everything's clean and dry down there so there's been no obvious overheating or wetting.

 

[Dec]

What’s the running temperature of the engine after about 3 miles, It should be a little over 80c?

Has the vacuum pump got a single yellow tube like below?

Dec

 

[Dec]

The air direction to the windscreen is controlled manually by two peg (see picture below) on the rear of the right side heater dial, there is no vacuum involved in there operation.

Sometimes, if someone removed the heater control panel, it can happen that the panel is not reassembled correctly in that two pegs aren’t put into the two tubes.
It’s explained in the thread below and might explain your fault.
http://www.mbclub.co.uk/forums/part...210-320cdi-avantgarde-estate.html#post2021143

Also… http://www.mbclub.co.uk/forums/electronics/29698-howto-replace-faulty-heater-panel-bulbs-w210.html


Dec

 

[mike18hc]

More vacuum pump information

The pump has two pipes, a yellow one and a clear one. The clear tube goes to the valve block port 1 in the engine compartment near the fuse box.
The locks all operate in about 1 second. Also the head rests drop correctly and the headlights move up/down as they should.
The pump buzzes consistently under only the following conditions. With the fan at 0, or at 1 to 5 with recirc on, the pump turns on after 5 seconds, buzzes for 3 seconds and stops for 1 second, ad infinitum.
Since I can find nothing else vacuum-related that produces this buzzing I assume the Recirc flap control leaks. So now I need to find the location of the flap control valve!
All the information I have found online appears to relate to LHD cars so can anyone help with my RHD model?

 

[Dec]

The fuel flap is also vacuum operated, is that locking/unlocking ok?

You could try disconnecting the Yellow vacuum tube and seal the end of the tube to make it airtight and seal where it enters the vacuum pump too, see if that changes anything, the pump will still run when you lock or unlock except the doors/boot and fuel flap won’t operate while the Yellow tube is disconnected from the vacuum pump. You could then try the same with the White tube.

Before you do the above, you need to make sure that you can open the boot/door lock with the emergency metal key blade before you disconnect any vacuum tubes, these locks are known to seize up.

Dec

 

[mike18hc]

Recirc operation seems the only culprit!

The pump's yellow tube functions ok and the pump's clear tube stops the buzz when blocked off. The valve block green tube to the flap block, when closed off, doesn't allow the pump to buzz, but of course in both situations there's no vacuum to operate flaps anyway.
I think this is the end of my investigations for the moment and I'll either not use recirc unless I'm choking or, in the spring, I'll search out the flap control block and try to trace the recirc actuator. At least the actuator's currently working even if it's leaking.
Does anyone know of a RHD equivalent to the US vacuum actuator layout drawing that seems to appear in most how-tos concerning vacuum problems? Or am I not looking in the right places?
Thanks to everyone for their inputs!

 

[Dec]

You could have as look inside the vacuum pump, below is how to open it.

On the reverse side of the Green PCB, in the picture above, there is an actuator that turns the pump motor off when you lock or unlock, the pump in the picture above has only one actuator because there is only one tube coming out of the vacuum pump, I think you may have two actuators, the same or different to the one pictured below.

Below is a thread that relates to how this particular (one Yellow tube) vacuum pump actuators work and how the can be adjusted, I don’t know how the internals are laid out in your particular vacuum pump (two tubes) but if you open it up then take some pictures so we can see what you have. Your problem might be related to the pumps electrics.

See… r129 central locking problem - Page 4 - Mercedes-Benz Owners' Forums

Its possible to run the central locking, with the boot open, and the vacuum pump “out of its box” so you can watch how it is being switched off and perhaps switch it off manually with your finger if the switch’s are similar to the one pictured above.

Dec

 

[mike18hc]

Still buzzing, but less of it!

I have looked into the pump and can see no problems with it.
The problem has altered a bit as it no longer buzzes every time the car's started, but it still buzzes for 10 seconds or so in little bursts more often than not.
Every vacuum-controlled feature looks to be working properly so there's no readily identifiable fault to attack.
I think I'll wait for something to change!

 

[Dec]

Is there a car alarm or any alarm dash light that might suggest that there is an alarm fitted that might be faulty.
Alarms are connected to the central locking system.
Any other keys with the car apart from the flip out key?

Dec

 

[mike18hc]

Back to the old buzzing

I spoke too soon. The buzzing when the ignition's on has restarted...most times at least. On one occasion it was directly linked with being in gear when stationary and engine running. Putting it in N or P stopped it. Then putting it in any gear started it again and so on! Now it regularly buzzes for 20 seconds or so when starting the engine.
It's also now intermittent when defrost is selected, sometimes it buzzes, sometimes not.
Is there a vacuum reservoir in this car and where would it be it it has one... in the wheel arch? I've looked at the online IPC and I can't really be sure if the 1995 model has one or not. There seems so many options around that time!

 

[Dec]

Is there a car alarm or any alarm dash light that might suggest that there is an alarm fitted that might be faulty.
Alarms are connected to the central locking system.
Any other keys with the car apart from the flip out key?

Dec

Not sure but I recall seeing something that might have been a vacuum reservoir behind the panel where the side indicator flasher is located, access via the wheel arch liner, driver side I think.

In any case, it’s more likely a fault with the vacuum pump unit given its random running.
You could take the pump apart, as it is illustrated in the last picture above and plug the electrical connections into the PCB, no need to remove any tubes to get the innards out of the case.

With the boot open, try lock/unlocking the car and do whatever is necessary to recreate the faults that cause the pump to run, you will be able to poke around while the pump is running.

Out of its box the vacuum pump wont shut off by itself as there is no suction/blowing pressure so in order to stop the pump motor you will need to move the “blade” switch at the Yellow arrow in last picture.
The pump PCB will be live so don’t let it touch metal or wet material.

I cant see a vacuum leak causing these mystery running’s, it all seems like an electrical fault.

Don’t let the pump run for more than 30 seconds at a time as it will get hot.

Dec

 

[mike18hc]

The central vent for fresh/recirc air doesn't open fully, well very little actually.
My wife reminded me of an irritating high-pitched intermittent whistle we heard behind the dash a while ago that's now stopped so chances are that actuator bellows is leaking.
I can get at the vacuum distribution block beside the fan so I'll try and block off the offending tube without damaging the pipe adapter. Then I'll know for certain why the vacuum pump's working so often and stop it burning out.

 

[mike18hc]

So, now I feel I've been misleading myself and anyone who's followed this thread. None of the vent flaps are inoperative and no bellows are leaking, despite what I said.
To update...now the pump cycles without end when the engine's running and the car's in any gear and is silent when in neutral or park.
Can anyone tell me what needs vacuum only when the car's in gear ? Help appreciated!!

 

[Dec]

What happens if you unplug the clear tube that connects to the vacuum pump, you will need to block the hole left by the removed clear vacuum tube.

Dec

 

[Codger49]

Pure shot in the dark as I don't know W202s, but many Mercs have a mechanism to lock the car doors when speed rises above 11 kph.

If yours has this, and it uses the vacuum locks, it might explain the engine running and not in neutral or park scenario.

 

[mike18hc]

Thanks for that. It's something I knew nothing about.
If the vacuum pump's running because something's leaking maybe this function wouldn't work. I wonder how to tell the difference between that and not having the function!
I'll think on that!