Looking for help with diagnosing AC noise

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Ray
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Looking for help with diagnosing AC noise

Post by Ray » Tue Jul 07, 2015 7:10 pm

1994 base 3000GT

AC cools as well as it did when new. Compressor itself seems to be working flawlessly.

There seems to be 2 noises, but may be coming from same location.

Noise 1-Metallic screeching noise when I turn on AC. It lasts for a long time. If I continually turn AC off and on, the duration is reduced and it usually goes away completely after the third/fourth engagement.

I also get the same metallic screeching noise if I rev the engine quickly.

Noise 2- Hard to describe, but almost sounds like a rattling sound. Always there, but seems to become louder when AC is on.

Anyone experienced anything like this? Troubleshooting ideas?

My best guess is tensioner pulley. If the clutch is gone, I would think I would not be able to cool the interior to an uncomfortable level.

Thanks

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curt_gendron
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Re: Looking for help with diagnosing AC noise

Post by curt_gendron » Wed Jul 08, 2015 11:43 am

Are you sure the noise isn't some kind of belt squeal? The accessory belt being a little loose is for sure the most common noise from that area. If it truly is a metallic noise, maybe have someone listen in the engine bay when turning the AC on and see if that helps isolate the noise. Sounds like you may need a new ac compressor? There is an idler and tension pulley on that belt too??

later,
Curt
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BluDevl
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Re: Looking for help with diagnosing AC noise

Post by BluDevl » Wed Jul 08, 2015 5:01 pm

It sounds like you have some A/C compressor clutch chatter. Completely normal, but somewhat annoying.

This usually happens as the A/C compressor clutch assembly wears and bearing play eventually happens. You are able to just have the A/C Clutch Bearing replaced, but it wont be cheap because of the labor involved.

I would recommend taking the belt off the A/C compressor, alternator, idler and tensioner pulley. Spin each pulley freely on that portion of the belt system and see if there is any play or noise is generated. Possibly replace the idler and tensioner pulleys so that they are new. Purchase a can of air from any electronics store used for cleaning keyboards and spray some into the area where the A/C clutch and pulley connect. This may remove any debris that could be trapped in there. Put on a new belt (since you have it off) and make sure the tension is set correctly. This is a manual tensioner assembly, so as the belt wears and stretches it should be adjusted and many people do not make these adjustments. If the problem still persists, more than likely it is the A/C Clutch Bearing that is causing the clutch to chatter.

Your A/C compressor is completely fine and would not engage or cool the vehicle if there was anything wrong the compressor. If the freon level was below what is suggested, or anything else was mechanically wrong with the compressor, the compressor would not engage as a fail safe.

Hope this helps.
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Ray
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Re: Looking for help with diagnosing AC noise

Post by Ray » Fri Jul 10, 2015 4:27 pm

curt_gendron wrote:Are you sure the noise isn't some kind of belt squeal? The accessory belt being a little loose is for sure the most common noise from that area. If it truly is a metallic noise, maybe have someone listen in the engine bay when turning the AC on and see if that helps isolate the noise. Sounds like you may need a new ac compressor? There is an idler and tension pulley on that belt too??

later,
Curt
Uh -this is embarrassing. Since I planned to replace the belt when I dug into this problem, I took my son's suggestion. I sprayed the belt with wd40 to see if the screeching noise changed. It never reappeared even during a 100 mile round trip to pick up a working compressor clutch and tensioner.

In the future, I guess I need to wear my hearing aids when attempting to diagnose noise problems.

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curt_gendron
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Re: Looking for help with diagnosing AC noise

Post by curt_gendron » Fri Jul 10, 2015 5:36 pm

Glad it was something easy. Here is a good page that shows how to tighten up that belt: http://www.stealth316.com/2-alt-drivebelt.htm" onclick="window.open(this.href);return false;
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