2001 Silverado 4.8 V8, High Pitch Air Release from AC?

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Beau63
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2001 Silverado 4.8 V8, High Pitch Air Release from AC?

Unread post by Beau63 » Tue May 27, 2014 9:12 pm

I'm getting a high pitch air pressure release noise like an , "Air Brake" from someplace in the front of the engine. It happens when the AC is engaged, defrost also. It doesn't do it when AC is off. Noise happens in an instant at rev RPM in park or during acceleration on the road. The AC pressures are all on specs and there have never been any problems with the compressor or system parts in the past. The compressor clutch cycles as it should. All lines are cold and hot as they should be to the touch during cycle. This started midway through last summer. The AC blows cold 40 degree air on the hottest most humid days. This noise is loud enough it turns heads when I'm passing people on the street. Hope somebody can help me out soon. :? :x :roll:


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carriedi
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Re: 2001 Silverado 4.8 V8, High Pitch Air Release from AC?

Unread post by carriedi » Wed May 28, 2014 2:20 am

noises are very hard to diag without actually hearing the noise. you're going to have to narrow it down. Try listening for the noise through a rubber hose or vacuum line. This way you can narrow down the area and maybe even find exactly where the noise originates.

you say the pressures look good but what are they? how much does it change when you rev it up and start hearing the noise? it's not the clutch slipping or the belt is it? Just in case... Some times the clutch will drag when the clutch coil releases it. the clutch springs get weak over time and will not release all the way so when the clutch cycles off it will give off a ringing sound. Watch the clutch to see what it is doing with someone in the car and rev's it up a little. does it make the noise when the clutch locks up or when it is released?
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Beau63
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Re: 2001 Silverado 4.8 V8, High Pitch Air Release from AC?

Unread post by Beau63 » Wed May 28, 2014 12:01 pm

Thanks for the tips. It's definately coming from the area near the EGR valve, just cleaned and inspected it, not the culprit. Thecompressor and clutch are cycling normal no hangup or belt slipping. Sounds like it's letting off pressure, just can't pinpoint it.

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carriedi
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Re: 2001 Silverado 4.8 V8, High Pitch Air Release from AC?

Unread post by carriedi » Thu May 29, 2014 3:59 am

you might want to do a backpressure test on the exhaust. just to make sure you don't have an exhaust problem.

If the ac system was venting pressure, it would be on the high side usually. If the high side gets too hot it could raise the pressure but if it were venting you should be able to find the leak and the ac would not have normal pressures. And if it were venting you would soon not be able to cycle the system on because there wouldn't be enough pressure to turn it on.

does it make the noise when the compressor clutch is engaged? When the compressor cycles and disengages is the noise still there? I don't mean when you turn it off. during the normal operation of the AC it will cycle on and off depending on the temperature and pressures. It will run for a while then turn off for a while. Does is make the noise under both periods or only when the compressor is running or only while it is off?

When the engine is on acceleration the computer may turn off the compressor clutch (WOT) to give the engine more power to accelerate.

I wish I could listen to your vehicle to try and hear the noise and verify where it might be coming from. you might want to take it to a shop where they could have someone just walk out and listen to it and just give you a visual (and audio) inspection on it to see what it might be.
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Beau63
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Re: 2001 Silverado 4.8 V8, High Pitch Air Release from AC?

Unread post by Beau63 » Thu May 29, 2014 9:23 pm

It was really hot and muggy here today, AC worked perfectly. It hasn't made the noise one time today. Stopped at my inspection guy's place, of course it wouldn't make the sound so he could hear it. More frustration!

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carriedi
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Re: 2001 Silverado 4.8 V8, High Pitch Air Release from AC?

Unread post by carriedi » Fri May 30, 2014 2:20 am

yep, that happens a lot at my shop too. they say it does it all the time but when they bring it in for me to hear or feel, everything works fine. Just have to wait until it's happening and take it in then
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Beau63
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Re: 2001 Silverado 4.8 V8, High Pitch Air Release from AC?

Unread post by Beau63 » Fri May 30, 2014 11:33 am

Yes sir!

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