I have an 07 5.9L, and when ever it is hot outside, and I turn the AC on, there is a loud bang and grind when the AC button is pushed. The AC still works good, and it doesn't make the noise after it has been engaged. It's been doing this for a while now, any ideas what it is, I'm thinking the clutch for the compressor is NFG?

 

I have the same sound and was told it was the compressor, but that it was normal.

 

Mine does this as well. Its not a grinding sound though. Just a thud.

 

Mine does the same thing. the dealer told me it was normal, it doesn't sound normal. If you turn the a/c off before you the truck down mine seems not to make the noise when i turn it back on.

 

my 04.5 does the same

 

Yep, my 07 5.9 makes the same noise.

 

Mine too, for 115K miles and works fine. Apparently it's normal for our trucks...just like the belt chirp on shutdown.

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Yep, mine too. Plus the chirp. Had to get used to it.

 

....same thing on mine since it was new

 

loud thud on mine too, since new, no problems though

 

Had the same issue on my '03 until the compressor finally failed. Installed new compressor and charged the system and not one odd sound out of it in over a year. It's definitely something with the clutch assembly in my opinion.

 

Its a pretty common thing, its because of the high compression of the motor that it engages the compressor like it does and the chirp on shutdown. Mine has done it since I got it.

 

It's the magnetic clutch on the A/C compressor. Mine has done it since new as well -- sometimes the belt'll squeak briefly as well when it's cold out.