A/C Compressor is loose!

[1995sierraz71]

I hope this is the right section. The truck I am referring to is a 1995 sierra z71 5.7 Manual. Last nite, we put a new compressor, condensor, high pressure line and accumulator in the truck. We vacuumed the system and refilled with proper amount of r134a and oil. The A/C blows nice and cold BUT.... when the compressor is running at idle, it makes a horrible rattling noise (very loud!). We thought the compressor was bad but when you push the top of compressor back, down, or to the side, the noise is gone. we have tightened the bolts pretty good, but the noise is still there. Is there any bushings/ supports that I may be missing or is there anything else i could do? Thanks in advance!

-Michael

 

[someotherguy]

There are steel bushings in the bolt holes that are sort of like shims; they take up the slack between the compressor and the bracket. If you remove the compressor from the bracket, generally it helps to push the bushings back out carefully so that you don't have to fight the compressor back in. I use channel-locks opened wide and a socket over the bushing for it to go into, and gently "grip" the bushings through, being careful not to tweak the bracket; that aluminum will break!

Also, there are tabs in the front of the bracket that are meant to correspond to the single ground-off flat on each of the compressor bolts. This is why you should never attempt to turn the bolts from the front; only remove the nuts from the rear - if you turn the bolt head you'll break those tabs and possibly the whole bracket. I would check that the bolts are properly seated as I'm sure many people install them and don't realize they need to clock each bolt so that the one flat meets up with the tab allowing the bolt head to sit flush against the bracket.

If this keeps up you might suspect your belt tensioner, absolutely if it's not the original Gates style unit - if you have one of those cheapo aftermarket ones that the bolt sticks way out in the front from the body of the tensioner, those are notorious for letting the belt set up an oscillating-like motion and it sounds all the world like a bad A/C compressor. This can be proven if you VERY carefully pry against the tensioner just a little bit with something like a broom handle, to keep it from bouncing around, the noise should stop. Obviously if you're not super careful this can be extremely dangerous, do so at your own risk. Or just accept what I'm telling you; if you see the tensioner start bouncing around side to side crazily when the compressor kicks in, replace it with a real Gates piece.

Richard

 

[1995sierraz71]

Thank you very much Richard, I will try that as soon as my next class lets out!

 

[skylark]

There are steel bushings in the bolt holes that are sort of like shims; they take up the slack between the compressor and the bracket. If you remove the compressor from the bracket, generally it helps to push the bushings back out carefully so that you don't have to fight the compressor back in. I use channel-locks opened wide and a socket over the bushing for it to go into, and gently "grip" the bushings through, being careful not to tweak the bracket; that aluminum will break!

Also, there are tabs in the front of the bracket that are meant to correspond to the single ground-off flat on each of the compressor bolts. This is why you should never attempt to turn the bolts from the front; only remove the nuts from the rear - if you turn the bolt head you'll break those tabs and possibly the whole bracket. I would check that the bolts are properly seated as I'm sure many people install them and don't realize they need to clock each bolt so that the one flat meets up with the tab allowing the bolt head to sit flush against the bracket.

If this keeps up you might suspect your belt tensioner, absolutely if it's not the original Gates style unit - if you have one of those cheapo aftermarket ones that the bolt sticks way out in the front from the body of the tensioner, those are notorious for letting the belt set up an oscillating-like motion and it sounds all the world like a bad A/C compressor. This can be proven if you VERY carefully pry against the tensioner just a little bit with something like a broom handle, to keep it from bouncing around, the noise should stop. Obviously if you're not super careful this can be extremely dangerous, do so at your own risk. Or just accept what I'm telling you; if you see the tensioner start bouncing around side to side crazily when the compressor kicks in, replace it with a real Gates piece.

Richard

I know that you had the 400 yard but your intimate knowledge always astounds me!

 

[someotherguy]

Thanks, I didn't just spend a few years tearing them apart, I've built a bunch of them too. Bought my first GMT400 in '99, the white '92 extended cab longbed. I've been in love ever since! Putting that one back together after it got stolen/stripped is how I ended up with a bunch of spare parts (bought 2 raggedy parts trucks) and started selling on CL out of my garage and a storage unit, it just eventually progressed into being a full-time biz with the shop and yard and buying up every beat-down 400 I could get my hands on and tow away. Still wish I'd never shut it down; I'd fire it back up but as much as I love these trucks I believe the time has passed for a GMT400-specific salvage biz, and I didn't really want to get into GMT800/900 as I really don't have the love for them at all.

Richard

 

[df2x4]

Still wish I'd never shut it down; I'd fire it back up but as much as I love these trucks I believe the time has passed for a GMT400-specific salvage biz, and I didn't really want to get into GMT800/900 as I really don't have the love for them at all.

If at all possible I'm going to keep my trucks for the rest of my life, you'd have at least one repeat customer if you opened it back up. Wish I could have witnessed a 400 only yard in person, I bet it was quite a sight to see.

 

[twil2922]

1995sierraz71, did you ever find the cause of this a/c compressor noise? I am having the same problem with my ac. Almost the exact same situation.