My '94 C280 has an intermittent vacuum noise inside the car. It seems to be coming from the passenger side rear. It only happens when my a/c or heat is on. Any ideas?

 

I am currently experiencing the same thing with my 1995 C220. I noticed after carefully observing that it's the vacuum pump that services the central lock(and, as I've found out from this forum, the air flaps of the vents, as well.) What happens is when I turn on the A/C and drive, and I stepped on the brake from a red light, I can hear the vacuum pump making a noise like the noise when it closes all the door locks. I am still investigating, I know it has to do with aleak in the vacuum, or maybe I'm wrong. In addition, the central air vents close whenever I turn on the A/C.

 

Sounds like you have a leak in the vacuum system for sure. The first post may be a more simple fix to a leak in the back door or the read headrest system. The second one may be a leak with the ventilation system in the dash. The latter can often be a massive hassle to fix. Do it yourself or plan on spending $$$ at the servicecenter. Download this tutorial to get an indication of what is involved. It is a very good tutorial but 15 mb in size:

http://www.savefile.com/files/627256

 

Thanks xvvvz. Can you give me any insight as to how to investigate the leak in the headrest or rear door?

 

hello jason im a new member with the same problem my back head rest wont drop down and ive read on this forum that there is a grey vacuum pipe near the air filter that could come off and also one in the boot area im going to check on my car i will let you know what i find my car is a 280 sport 1995 c class