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  #1  
Old 08-05-2008, 11:53 AM
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A/C noise?

The A/C in my car works great but when it is on and I am at a stop the compressor makes a knocking sound that is loud inside the car. The sound goes away as soon as the rpms pick up. Any one know if this is normal? Any one know why it does this?
Even when it is making the noise the A/C is working fine.
Thanks

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  #2  
Old 08-05-2008, 01:23 PM
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Quote:
Originally Posted by Phil View Post
The A/C in my car works great but when it is on and I am at a stop the compressor makes a knocking sound that is loud inside the car. The sound goes away as soon as the rpms pick up. Any one know if this is normal? Any one know why it does this?
Even when it is making the noise the A/C is working fine.
Thanks
The short answer is no, its not normal. First off, are you certain its your A/C compressor? Pop the hood and verify that's where the sound is coming from. Any sounds being emanated from an A/C compressor are usually a sign of it being on its last leg.

Being that it happens at idle and goes away at speed could indicate a high side pressure problem if your auxillary fan isn't working. When you come to a stop your high side pressures rise because your auxillary fan isn't sending air across the coils. When you speed up you get air flow over the coils and the pressures go back down. High pressure could cause your compressor to lock up and possibly make weird sounds. Is your auxillary fan working?

I'm just guessing here.

Scott
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1982 Mercedes 240D, 4 speed, 275,000
1988 Porsche 944 Turbo S (70,000)
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Old 08-05-2008, 02:09 PM
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Good point. I'll check. This has been going on for 2 or 3 years now. If I am at a stop and the A/C is on and I turn off the A/C it stops right away.
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Old 08-05-2008, 02:12 PM
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Originally Posted by Phil View Post
This has been going on for 2 or 3 years now.
And you just now decided to check on it?! Better late than never I guess. If its been going on that long and nothing has self-destructed, it probably can't be that serious.

Scott
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1982 Mercedes 240D, 4 speed, 275,000
1988 Porsche 944 Turbo S (70,000)
1987 Porsche 911 Coupe 109,000 (sold)
1998 Mercedes E300 TurboDiesel 147,000 (sold)
1985 Mercedes 300D 227,000 (totaled by inattentive driver with no insurance!)
1997 Mercedes E300 Diesel 236,000 (sold)
1995 Ducati 900SS (sold)
1987 VW Jetta GLI 157,000 (sold)
1986 Camaro 125,000 (sold - P.O.S.)
1977 Corvette L82 125,000 (sold)
1965 Pontiac GTO 15,000 restored (sold)
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  #5  
Old 08-05-2008, 02:29 PM
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A belt a little loose can do that also, as can a failing clutch pulley bearing.
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  #6  
Old 08-05-2008, 10:29 PM
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Is the compressor secured bolted to the related brackets or engine block?
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  #7  
Old 08-06-2008, 10:36 AM
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Originally Posted by TOPGUN View Post
Is the compressor secured bolted to the related brackets or engine block?
I ran the system last night and the condensor fan runs fine, the belt looks ok but whips a little so the next thing is to figure out how to adjust the tension. I see a tension adjustment but I'll need to get under the car to find out where to loosen the piviot points. Also I want to remove the belt and try moving the clutch pulley to see if the bearing might be going or if the mounting bolts for the pulley might be loose.
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Last edited by Phil; 08-06-2008 at 10:51 AM.
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Old 08-06-2008, 11:50 AM
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if the belt has been whipping for 2 to 3 years, just replace it. a new belt will be stiffer, and you can adjust it properly too.
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Old 05-24-2009, 03:54 PM
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I must admit that I was skeptical that the noise seemingly coming from bad bearings in the compressor would be caused by just a loose belt - but sure enough - that is all there was to it! Again I saved bunch of money and had a good time!

This is such a great place to find answers to life's important questions!Thank you...

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