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A/C Compressor Vibration

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Old 08-20-2018, 12:36 PM
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Lawman31
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Default A/C Compressor Vibration

Hey all,
So when I accelerate and hit about 3,000 RPMís, I get a noticable vibration, but if I turn off the A/C, it isnít there. Do I just need a new bearing in my A/C compressor clutch? Has anyone experienced this? Everything works fine and the clutch isnít noisy or anything, so perhaps itís just starting to go bad?
Thanks...
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Old 08-20-2018, 04:02 PM
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Are you running headers by chance? We have ran into issues when headers are installed and the support bracket from the A/C Compressor is not reinstalled to the exhaust manifold (now header) leading to vibration issues.

Colton @ CSM Performance LLC
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Old 08-20-2018, 05:06 PM
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Originally Posted by CSM Performance View Post
Are you running headers by chance? We have ran into issues when headers are installed and the support bracket from the A/C Compressor is not reinstalled to the exhaust manifold (now header) leading to vibration issues.

Colton @ CSM Performance LLC
Thanks Colton, no headers my car is 100% stock. The vibration isn’t crazy bad, but noticeablly different with the compressor turned off. With out the compressor on the acceleration upto and past 3,000 rpm is smooth and normal, but with the compressor on there is a noticeable sound generated from the engine compartment that would be best described as a slight vibration. It doesn’t shake anything badly and you don’t really feel it too much, just slightly in the seat of your pants and the noise from whatever it is is more anoying than any vibrations that you are feeling.

Hope that makes sense.

I had a shop look at this and they told me that they thought it was due to a bad engine mount, so I replaced both engine mounts, but even though one of the engine mounts was cracked and needed to be replaced, this didn't resolve this issue. Since I have it isolated to the A/C compressor for the most part, I figured that would be the best place to start. Either the drag from the compressor is causing a vibration in another area at 3,000 rpm’s or it has something to do with the compressor directly. I can’t really think of anything else it could be at this point really.

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Old 08-20-2018, 05:57 PM
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not long ago, there was a thread on a similar subject -- https://www.corvetteforum.com/forums...-thoughts.html . I seem to recall, folks thought it had something to do with a cracked compressor mounting bracket . not sure what year you're running, but check for the overall alignment of the compressor/bracket, loose hardware, and any issues with the mounting bracket itself. inspect your compressor clutch assembly. some folk added an additional bracket to the assembly. not sure if it has any actual benefit or just the placebo effect.
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Old 08-20-2018, 06:19 PM
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Will it still cause the vibration if you free rev it, IE. not under any load?
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Old 08-20-2018, 07:13 PM
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Originally Posted by CSM Performance View Post
Will it still cause the vibration if you free rev it, IE. not under any load?
This question needs an answer, because its the right question.
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Old 08-20-2018, 07:39 PM
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Originally Posted by CSM Performance View Post
Are you running headers by chance? We have ran into issues when headers are installed and the support bracket from the A/C Compressor is not reinstalled to the exhaust manifold (now header) leading to vibration issues.

Colton @ CSM Performance LLC
I have a 91 and there are 2 braces on top that are real easy to see. It was the 3rd one that wasn't there when we transferred the motor over. Ran quite a few years before it broke. Replace the bracket and it broke again within a year. Found the 3rd brace on eBay and no more breakages. HOWEVER, the 3rd Brace didn't really make a night and day difference on my 91 BUT I have a 383 with LT headers so a lot of noise. Still, if he does have the 3rd brace for his version but does not, I would say he needs to get it. Not sure about his year.
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Old 08-20-2018, 08:49 PM
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Thanks everyone for the excellent feedback, I found the problem. Recently I had the engine rebuilt and the mechanic forgot to install the rear bracket. I went to see him today and low and behold he had my bracket and installed it. A little frustrating, but happy I was able to figure this out....





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Old 08-20-2018, 09:39 PM
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That bracket is rather important for the structural integrity of the alternator and A/C Compressor position. Make sure to check your belt as well as there could have been a slight misalignment leading to belt wear without that bracket. Glad you solved it
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Old 08-20-2018, 10:01 PM
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Originally Posted by CSM Performance View Post
That bracket is rather important for the structural integrity of the alternator and A/C Compressor position. Make sure to check your belt as well as there could have been a slight misalignment leading to belt wear without that bracket. Glad you solved it
Is it enough to cause that much vibration that can be felt? Reason I ask is that last year, I had enough that I could hear it only with the hood off and when the compressor engages and a couple weeks ago, I had to start gathering stuff for a "Compressor Party". You see, the compressor got noisy and crapped the lines where we can see stuff in the orifice. Question I have is whether the OP is hearing vibration from having one brace less or whether the compressor is about ready to go
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Old 08-20-2018, 10:31 PM
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Originally Posted by aklim View Post
Is it enough to cause that much vibration that can be felt? Reason I ask is that last year, I had enough that I could hear it only with the hood off and when the compressor engages and a couple weeks ago, I had to start gathering stuff for a "Compressor Party". You see, the compressor got noisy and crapped the lines where we can see stuff in the orifice. Question I have is whether the OP is hearing vibration from having one brace less or whether the compressor is about ready to go
Could be a mix of both. I had the same problem on my car when I installed LT and didn't put the auxiliary brace back on to the exhaust manifold (now headers). Once I reinstalled the brace (had to make spacers off the headers) it solved the problem all together. I would venture to say the bracket the OP was missing is much more structural than the one I didn't reinstall and had problems with. Just an educated guess but the compressor could also be failing, only time will tell.

Thanks!
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Old 08-20-2018, 11:18 PM
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Originally Posted by CSM Performance View Post
That bracket is rather important for the structural integrity of the alternator and A/C Compressor position. Make sure to check your belt as well as there could have been a slight misalignment leading to belt wear without that bracket. Glad you solved it
Thanks... Yes, that bracket seems to be a very important part and him not putting it back on was a big mistake on his part. I lost faith in his abilities today and find that I have little trust in his work now. I am glad that I watched the rebuild at each step to ensure that the major work was done right. I just put a new belt on last week, so it should be okay, but Iíll take a close look at it. The one I pulled off was a little cracked, but things seem to be alligned.
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Old 08-21-2018, 07:17 AM
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Originally Posted by Lawman31 View Post


Thanks... Yes, that bracket seems to be a very important part and him not putting it back on was a big mistake on his part. I lost faith in his abilities today and find that I have little trust in his work now. I am glad that I watched the rebuild at each step to ensure that the major work was done right. I just put a new belt on last week, so it should be okay, but Iíll take a close look at it. The one I pulled off was a little cracked, but things seem to be alligned.
Anyone can make that mistake. I wouldn't hold that against him. That said, that he knew the mistake but didn't fess up till you confronted him, well, that I can't deal with.
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Old 08-21-2018, 08:58 AM
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Originally Posted by aklim View Post
Anyone can make that mistake. I wouldn't hold that against him. That said, that he knew the mistake but didn't fess up till you confronted him, well, that I can't deal with.
I would.

A jigsaw puzzle wont have leftover pieces, neither will mechanical service.
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Old 08-21-2018, 10:21 AM
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Originally Posted by aklim View Post
Anyone can make that mistake. I wouldn't hold that against him. That said, that he knew the mistake but didn't fess up till you confronted him, well, that I can't deal with.
The guy means well, but has too many irons on the fire and tries to take shortcuts when he runs out of time I think. The bolt hole in the compressor and head, so 2 of the 3 needed to be tapped since the threads were a little messed up. Yesterday he couldn’t find a tap since he is so un organized, so I suggested making one from a spare bolt, which he did. It took him about 30 minites to get that bracket back on and think at the time he finished the motor, he didn’t have time. In other words, I don’t think he left it off on accident.
While at his shop yesterday I found another bracket that looked like it was from my car also, and looking at this diagram last night, I found that the small gap between the bracket he just installed and the altenator should have another bracket. I am going back today to see how this bracket fits. I looked yesterday and couldn’t see how it could fit, but this diagram should help. He told me that the second bracket wasn’t for my car, but I am pretty sure it is. Bracket #5



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Old 08-21-2018, 12:17 PM
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Originally Posted by Lawman31 View Post


The guy means well, but has too many irons on the fire and tries to take shortcuts when he runs out of time I think. The bolt hole in the compressor and head, so 2 of the 3 needed to be tapped since the threads were a little messed up. Yesterday he couldnít find a tap since he is so un organized, so I suggested making one from a spare bolt, which he did. It took him about 30 minites to get that bracket back on and think at the time he finished the motor, he didnít have time. In other words, I donít think he left it off on accident.


Sloppy and lazy. Dishonest to boot. Thanks but I think we should be looking for someone else to do anything Didn't make a mistake Took shortcut and tried to cover it up. Regardless of skill or price, I'd pass on him altogether even if it is an oil change
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Old 08-21-2018, 01:08 PM
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Originally Posted by aklim View Post
Sloppy and lazy. Dishonest to boot. Thanks but I think we should be looking for someone else to do anything Didn't make a mistake Took shortcut and tried to cover it up. Regardless of skill or price, I'd pass on him altogether even if it is an oil change
Yes, I agree and that is exactly what I will be doing. This is a picture of the other brace I need to go get from him today... I will put it on myself. It's the one on top shooting off to the left to the back side of the altenator. I saw this brace at his shop yesterday and asked him about it and he said that it was not for my car. And this guy has 30 years experience? I am done with him at this point.


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Old 08-21-2018, 01:52 PM
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I don't like to deal with crooks so I avoid them whenever possible. 2 years experience and honest beats 100 years of experience in the field and dishonest. I never trust any mechanic until I build up trust .Small projects with me watching and so on.
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Old 08-21-2018, 03:14 PM
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Originally Posted by aklim View Post
I don't like to deal with crooks so I avoid them whenever possible. 2 years experience and honest beats 100 years of experience in the field and dishonest. I never trust any mechanic until I build up trust .Small projects with me watching and so on.
I agree....
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