I have replaced the A/C compressor three times on my '86 vette, along with the belt tensioner, water pump, alternator, and just yesterday, the air pump. There is a strong vibration coming from the accessory belt system (not the motor) at or just above idle with the compressor running.

I have removed and replaced all of the these components and the related brackets, making sure everything is tight. I have even added brackets to the power steering pump that GM added to later L98's in an attempt to quiet the problem. I also installed a "frisbee" from an '88 - now that is getting desperate! Still no luck at all. I posted this problem a month or two ago and only got a few responses. C'mon guys, I can't be the only one with this problem!



[Modified by vetracer, 11:53 PM 9/25/2002]


[Modified by vetracer, 11:54 PM 9/25/2002]


[Modified by vetracer, 11:55 PM 9/25/2002]


[Modified by vetracer, 11:56 PM 9/25/2002]


[Modified by vetracer, 11:58 PM 9/25/2002]

 

ok, well now that you have done all the obvious, its time for the not so obvious items.

1 did you put a new compressor on or just take the old off and put on again
2 check your clutch assembly on the compressor, make sure it is turning true and is not warped. make sure the belt is straight/perpendicular in the groves.
3 is the vibration the same as befor...better...worse.
4 how did you charge the system after reinstall...what is you pressures of the refrigerant at idle....does the gauge mimic the vibrations. overcharges and air in the system will cause the compressor to work harder than it should and will cause pulsations. when they get too high, it may be being transferred to the engine components.

since you say it only occurs with the a/c on...the clutch pulls in, rotates the compressor, pumps refrigerant from low to high side...it is a constant volume system. does the vibration go away at or over 2000 rpm.

also CHECK each of your pulleys for out of round or eliptical pattern..that will cause a vibration at its natural frequency if something is exciting it. any pulleys loose..sure you have checked that by now but recheck for roundness

you can send me email if you want to discuss this in greater detail. good luck. Tom


[Modified by C4TOMCAT, 7:21 PM 9/25/2002]

 

Did you put a new GM serpentine belt on?

I think the belt brand makes a big difference because all L98's do this otherwise.

 

Your not the only one with this problem. Mine does exactly the same thing.

Although, it "used" to not do this. When I had the AC Delco compressor on... there was never a vibration. One day the SC belt shredded and took out the little connector on the AC Coil. So, I just bought a new coil to put on it. $100 in tools, and about an hour later, I got this big Whoosh sound when I removed the wrong spring clip from the compressor. Dummy me pulled the seal retainer out, and she spit freon and oil everywhere.

Anyway, the point I'm getting at... I didn't opt for the $300 compressor from Chevorlet... but got a "Factory Air" Reman. for $99 at Parts America.

Ever since then... at or just off idle... I have this vibration...that comes and goes. Almost like a "Buzzing". I looked up close at it... and I swear that Its the belt slipping on the Alternator when the Compressor clicks on. I am thinking that vibration is coming from a belt slipping...but trying to grab. I am just dealing with mine for now, but I am thinking that the tensioner is shot.... although you said you tried that.

If you put a new AC on yours... was it new? Reman ? If it was Reman... did you dump out all of that oil in there? Mine came out on accident... but GEEZ was there alot of oil in there... thick too. You might try pulling a vacuum on it and have it charged with the correct amount of oil charge. I am thinking that it is something to do with all that oil they put in there.

Just some info... good luck with it. But after its all said and done... sounds like my problem... and I am almost certain that its the belt "kinda" slipping.... compared to wheel hop when doing a burnout.

Doesn't do it at higher RPM's cause your belt tightens as you rev on the AC side of the crank.

 

I have the same vibration above idle when the A/C is on. It's strange, I have replaced the serpentine belt with a Brand new GM belt, still to no avail. I pinpointed the vibration to the cover over the Distributor, and shimmed it up, but I still feel vibration. I dunno, I just live with it...

 

Thanks for the info. Maybe we are having the same problem because our cars look so much alike? (red, factory wheels) You have a good point about the compressor. All three compressors have been remanufactured components from CarQuest which could indeed be the problem. This time around I did not evacuate the system because the old compressor wasn't coming apart, just noisy at the clutch and seemed to have excessive play in the pulley.

My latest desperate solution was going to a wrecking yard yesterday and pulling all of the brackets and bolts from a '91 L98 which uses the newer style Nippondenso compressor. Since fall is here and I won't be using the A/C and I am planning to build a 383 with a mini-ram over the winter for the car, it would make sense to update the compressor as well. It appears from your username that you have a 383 in your car. How do you like it?

 

I'll check those items out, C4Tomcat. Thanks for the new ideas.