there is a rattle at idle with engine hot or cold when I turn on the ac this truck has one serpentine belt which runs ac,water pump . power steering ,idler pulley , tension pulley, and crank shaft. the rattle is all but gone when I come 100-200 R.p.m.s off idle.
I thought the compressor was bad, so I installed a used one TWICE !! same problem.
so I bought a new/reman. unit also changed the orifice tube, and receiver dryer
flushed system added new oil for R134A and weighed in charge after pulling system down to 500 microns of vac. all 4 compressors cooled beautiful no problems other than this Rattle I have changed the belt and both idler pulleys power steering is quiet when stethscope is used as is the water pump .
could the load from ac cause something in engine to make this rattle !!!???????

engine runs great , auto transmission shifts well , uses no oil I even checked the cat.converter=ok odometer broken guessing close to 100,000 miles

Gees! Get a stethoscope and fix the bearing causing the problem and quit throwing parts at it!

T
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Tom Greenleaf - MetroWest, Boston

The noise most likely has nothing at all to do with the A/C. The fact that the compressor is pumping causes a jerking action to the belt and that's what brings out the noise.

There are a couple of things to look at

1. Torque converter bolts........ make sure they are tight and try to look up at the flywheel/flexplate for any cracks that would show up as rusty spots.
2. Harmonic balancer....... make a mark on both the inside and the outside that align with each other and run the engine. shut it off and see if the marks still align.
3. The belt itself.......... I have run into time when the belt is just a little too long and it causes the tensioner to hit against it's stop. Once the compressor starts pumping, it will just rattle against it's own stop.
   

78 Corvette Pace Car For Sale-18k mi orig-Florida