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Old 09-09-2006, 11:51 AM
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ILUVMILS ILUVMILS is offline
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Join Date: Sep 2002
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I get a few of these every week. Not just ML's either. 203's, 211's, 220's, etc. It seems that MB has figured out a way to reproduce a "P/S pump type" noise from the A/C compressor . The way we diagnose it is simple. You'll need MB poly-belt #011-997-96-92. Just install this belt in place of the original, leaving the A/C compressor out of the loop. For diagnostic purposes, the engine can be run in this condition with no problem. If the noise goes away, the compressor is to blame. This procedure works on M112 and M113 engines.

As far as ML's go, I replaced a noisy P/S pump once, and the noise was still there. I looped the A/C compressor out, but the noise didn't go away. I drove it around for awhile to make sure all the air was bled out, but no luck. I was certain the noise was coming from the new pump, so I ordered another one. The next day, when I started it up to drive it into the shop, the noise was gone. Nothing. Not even a hum. I guess some air was trapped and it just rose to the top while the vehicle sat overnight.

Anyhow, the trick with the belt works great. MB dealers all over have been doing it for years. Good luck
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