1996 C220 - Vacuum Pump Problem
 

Just purchased a 1996 Mercedes C220 and am really happy with it. Just have one minor problem that I'm hoping I can solve without having to take the vehicle to the dealership service department.

I've recently noticed that my trunk mounted vacuum pump stays on for about 10 minutes after I start the vehicle. I find this strange because I have had no problem with the remote locks. The noise can be heard when the car is idling low. The pump will run for short intervals--4 seconds on, then 4 seconds off. After about 10 minutes of driving, it goes away. Today, I disconnected the pump in fear that I will burn it out. Are there any electrical relays or components that could cause this to stick? I know the problem is not the pump. Today I tested a used pump in the vehicle and got the same result.

This website rules! Thanks in advance!

You've got a vacuum leak somewhere... is it every time the doors lock?

There is a translucent vacuum line that goes from the pump to a vacuum manifold under the hood that helps the engine vacuum keep all of the A/C vacuum elements working. IF you have a leak in the A/C system, the vacuum pump will run as you described that yours is running.
Try pushing the EC button with the temp set at 72deg & see if the pump stops running. IF so then the fresh air vacuum element is leaking!! Good luck.

Sorry it took me so long to get back on here. Thank you both very much.

The problem occurs even when the locks aren't used.

I did try setting the temperature at 72 and the control to EC. The noise did go away. But then I noticed that it goes away when set at any temperatue and whether the EC button is depressed or not. As long as the fan is blowing, it doesn't happen at all! I'm puzzled but not as concerned since this will serve as a temporary fix.

Any other info would be appreciated. Does it sound like an air leak?

buzzing sound in the rear boot
 

I also have this problem in my 1994 C180 Euro version and the sounds are the same rythmic buzzing after you start the engine and lasts for about 5 to 10 minutes whether you have the A/C on or not. 2 shops have looked at this but cannot find the vacuum leak and have been only too eager to swop a new A$1200 vacuum pump at my cost without any guarantee that this will solve the problem. Once installed, they won't remove it and replace the old one. Also all the time you are paying for their labour at such exhorbitant rates. Can someone out there pinpoint the exact cause for all of us sufferers? Thanks.

vacuum, pump
 

I had the exact same problem, however my pump has since died. Its from leaks in the wiring I was told. If anyone has any diagrams of the wiring, please share. I don't want to tear my car apart following the mini hoses. Also if anyone knows a cheap source for these vacuum pumps or a rebuilder, please contact me. thanks.

Vacuum system leaks
 

Hi there, this seems to be a very common problem in the Merc cars due to the use of vacuum hoses to make things work when they could have been more advanced by using other stuff like switches, magnets, relays, small electric motors. My 1994 C180 had this problem, but it cost me more than A$1000 to have my indie sort things out. Noise gone, same old pump, only leaks under the dash fixed by changing 2 of the rubber/plastic vacuum open/close units. The rubber gaskets were worn and holed. This also caused some aircon circulation problems. Now, the rear headrests still work, but the aircon has started to pump only when I release the accelerator. On acceleration, the fan and compressor stalls, real crazy. My 1997 C180 has a similar problem with one of the headrests, but another indie took only a couple of hours and found the culprit( same little plastic socket with rubber bellow gasket inside) and changed it for free without having to remove the whole dashboard which was what cost all that money in labour time and some very cheap stuff like screws and washers and things that were lost or missplaced. Good luck in your search, now you know what to look for , so tell your indie or stealer what to look for, those items only cost about $15 each, not the $1000 vacuum pump they so eager to steal from you! Cheers!

But how can you still test to see if you vacuum pump is alive not dead?

Vacuum leaks in Benz cars
 

:mad: I don't know how you gonna test them, but if you switch on the ignition keys and start the engine, some vacuum will be created in the system and then press the rear headrest switch, making sure that you have raised both of them to upright position and see if they both fall together almost. If so, then your vacuum system should be ok. How ok it is I won't know because this vacuum circuit controls a lot of other things in the car, maybe even the doors and the aircon system and the air-circulation system in the car. Try to listen for the whirring sound coming from somewhere in the rear boot next to the fuel inlet, under it. This is the vacuum pump location. If its noisy, its going out soon. Sure to be leaking somewhere. There can also be another whirring or buzzing sound, but that is the fuel pump under the car near the right wheel(or left). If thats making noise, then thats also going too. I'm no expert, but hear this from many people with the same problems. Good luck.