AC Rattle?

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my name is alex

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I have a fairly loud rattle coming from the compressor (or that area). The rattle stops within a second or two of turning off the AC. Any thoughts?

I only noticed this because I realized yesterday that the rear is not blowing cold, so I was about to try and diagnose whether it was a blend door issue or orifice issue. Front ac is still cold.

This compressor is just two or three years old.

While I didn't notice it while driving from the cabin, it's a rather pronounced rattle when listening outside the truck.
 
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someotherguy

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Going to assume this is the 1999 454 in your sig. If you were a TBI I'd ask if you had an aftermarket belt tensioner as the cheapie one is bad about oscillating in a way that sounds a lot like a failing compressor.

So does it rattle only while the compressor is engaged? Watch it long enough to see the clutch engage/disengage and see if the sound follows.

Compressor 2 or 3 years old...a rebuild? Most don't have too good of a reputation. Use a mechanic's stethoscope with the A/C running and listen around the engine bay, including touching onto the compressor body (obviously, be careful of any moving parts) and you should be able to tell where the sound is coming from. Those HT6 compressors used on Vortecs are bad about leaking at the seam where the case halves meet, as you probably already know. Signs of grime around that area would indicate a leak, as the oil escapes the compressor, with the refrigerant not far behind.

Richard
 

my name is alex

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Thanks Richard. It's a brand new compressor installed July of 2015. No aftermarket tensioner as far as I know of, and yeah, it only rattles when the ac is on - though I haven't tested enough to see whether it goes off once the compressor cuts out with the ac still on. I'll go check that out.

Compressor still looks new, with no apparent leaks. I see SMP Temp written on it. The rattle sounds like metal on metal to me and the frequency of the taps increases when I increase RPMs.

In terms of the blend door vs orifice issue, I'm not sure which two lines on the passenger side to check. There are two coming out an opening in the frame right under the front passenger (one is hot and the other is warm), but then there are two above that coming from further forward on the truck (the fatter one of these is cool while the skinny one seems to be ambient temp).
 
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Rock Hard Concrete

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My factory tensioner rattled and it would go away with the ac on so i removed it.... after realizing the noise was still there I replaced the tensioner. No more noise but quite interestingly the new tensioner has only half the force of what the factory was...
 

my name is alex

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My factory tensioner rattled and it would go away with the ac on so i removed it.... after realizing the noise was still there I replaced the tensioner. No more noise but quite interestingly the new tensioner has only half the force of what the factory was...

Thanks Mike. I'll have to figure out where the tensioner is and check it out.

Oddly enough, I couldn't get the compressor to disengage yesterday...
 
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