Space387

While working on my 90 coupe I retrofitted the R12 system for R134 and went through the process of vacuum testing and charging it. Now the AC works great and no issues up to about 3000rpm where a vibration sets in. If I turn off the AC it goes away. The vibration is progressive and builds with rpm.

Has anyone had an issue like this or have an idea what this could be? Maybe i overcharged it? There is not a lot ofbbninfo on how much R134 the car needed, that I could find, so I'm not sure at this point.

PatternDayTrader

A lot of these sorts of problems up being a cracked mounting bracket for the compressor. So inspecting that closely first, is my vote.

Space387

I will check when I get home today. In terms of gross damage I have had the compressor off for about the past month working on another issue and did not see any large cracks, discoloration or deformities but I'll look for anything like a hairline crack.

Any other potential issues while I'm under the hood?

WVZR-1

You need to be sure you're using the complete set of support/braces for the compressor mounting. Have you installed headers?

there's many posts scattered throughout the C4 section for busted/cracked A/C mounting brackets. A search for 10105236 in the C4 section should give you a few mounting images from GM SPO. I know I've posted them a few times. Your problem has been experienced by many!!

use the 'SEARCH THIS FORUM BUTTON' from this link.

https://www.corvetteforum.com/forums...-1984-1996-19/

Space387

Looking at one of the threads I found a diagram with an extra brace I do not believe I have. One more thing to check for when I get home.

3D-Aircrew

You need to be absolutely certain on your pressures because if you are wrong the compressor can grenade and even put a hole in your hood.

Space387

it was in fact the bracing. Found the missing one I misplaced and the vibration is gone