Horrible grinding noise - Can't seem to figure out

[94OldRed]

So a couple of months ago I was getting a horrible grinding noise when I turned on the AC. I didn't think the problem needed any further diagnosing, I just went straight for AC compressor. Well I just recently changed it with a brand new unit, and the problem still exists, a terribly loud grinding noise while the AC is on. Now it's only there when you turn on the AC, as soon as it's off everything sounds just fine. So I'm thinking to myself there's no way this brand new compressor I installed is bad too! I did a full flush, filled her up, and it blows ice cold.

Any ideas on what else it could be? Again, when the AC is off, all the other accessories and pulley's sound 100%, no squeaks anywhere. With it on, the noise is there, but it almost sounds like it may not even be coming from the AC compressor, it's hard to pin point with all the engine noise. Almost sounds like it's on the drivers side, maybe the alternator? Is it possible that when the AC is on it puts a strain on the serpentine system and is causing something else to produce the noise? What do you guys think?

Oh ya, my truck is a 1994 K1500, TBI 350 with a whipple supercharger.

 

[montess85]

I assume the new compressor came with a new ac clutch?

 

[someotherguy]

With the Whipple kit on the TBI engine, does that replace the OEM tensioner? Or more to the point, if it retains the original tensioner setup, do you still have the OEM unit or an aftermarket replacement?

Here's something to try regardless, but you have to be ridiculously careful doing it. Get the engine running, A/C off, and have a helper ready to turn it on for you. Have a piece of broomstick, wooden rod, long pry bar, whatever handy. Have your helper turn the A/C on, while you observe the tensioner. Do you see it oscillating back and forth a bit? It should do this a little bit, but if it's bouncing a lot, it's an issue. VERY VERY VERY carefully reach in with it to press against the arm of the tensioner to steady it. If pressing against it to keep it from moving shuts up the noise, you've found the problem.

I've seen this at least twice that I can recall. Friend of mine bought one of those crappy aftermarket tensioners and it went nuts with the A/C on. Also had a customer that came to me for an A/C compressor, I usually didn't sell them because you can't trust a used one. This guy was bucks-down and desperate so I took one that I knew was working and sold it to him cheap. He called me and said it was still making noise like the compressor was bad, although he saw that one running quiet on the parts truck. I told him to bring me the truck, we fired it up, and I saw he had one of those same aftermarket tensioners - brand new - and it was bouncing all around with the A/C on. I steadied it with a pry bar and the noise instantly went away. Swapped it out with a used OEM (Gates) tensioner and all was well.

This Vatozone piece was the offender in both cases, brand new:

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And this is what cured it in both cases, used OEM/Gates type:

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I know it sounds nuts but the noise it made sounded so much like a bad A/C compressor, it was uncanny.

Richard

 

[Rusty Nail]

My thought was also the tensioner.
They have marks on them what indicate acceptable "usage range". It may be that bearing though and not the spring. They're cheap.

 

[94OldRed]

You know, I didn't really think about that. I used the old one that was included with the used whipple kit I bought, and for the longest time it sounded just fine. I did go buy a new vatozone tensioner because I thought the old one was wore out, not based off the sound though, but based off it looking like it was making contact with the bracket. I modified the bracket and bought the new tensioner and now I know for a fact it's not making contact anymore.

Bad thing is, is that the whipple kit does not re use the OE style tensioner. It uses what I believe is a C4 corvette style tensioner. It looks like this.

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Except it was autozone brand so it has the black plastic spring housing instead of metal. Maybe I should look for an OE tensioner instead of that autozone crap, if they even still make them.

 

[someotherguy]

It's something to try...Gates will have one available, you just need to figure out what year to buy for. Since C4 started with the Crossfire Injection, went to TPI, then LT1, etc. so the tensioners probably vary across the board as the accessory drive likely changed.

Richard

 

[Rusty Nail]

Ruh-roh! I think we may be on to somethin!
Previous bracket mods relating to tensioner malfunction? Yes please!

I'm willing to bet that you have not ever run the correct one for your application and the fix is something you have never used before. I wanna hear about undoing the bracket mods!
A call to the blower company will be time well spent.