what is it?
 

1995 s320
:stupid: today I pulled into a parking space everything was fine , a couple hours later I went to start the car and heard a squealing noise under the hood.
facing the engine on the left side was a pump of some kind that was frozen so that the belt spun around it but the pulley didnt move, i'm trying to identify what its function, it has a black u shaped rubber hose coming out of the rear like a discarge or vent of some type, it's not the alt or a/c compressor or water pump which are all driven by the same serp. belt. I'm guessing that it's a vacuum pump of some type sets just to the side of and a bit lower than the air box for the air cleaner, or perhaps its a smog pump i really dont it seems to have a vacuum line coming from it but only one and it is small (1/4 in).does anyone know what the funtion of this pump is?

part
 

what you are looking at is probably the air pump not a vaccum pump
it is for the emission's controls

Thanks
 

thank you, i found one on the net and will change it as soon as it comes in. I must have been brain dead not to think of smog pump, its hell getting old, I looked and found alt, p/s pump a/c compressor and water pump, by following the pulleys but never thought about the smog pump. DUH!, I'm in california the state with the grey sky. yOU WOULD THINK THEY WOULD LAST LONGER THAN 170K, being a Mercedes and all. I wonder what is chronic to fail on these things, I just had to replace the coils, but the wiring and evap are working, at least they were untill I said something