AC compressor rattle

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gyver

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Year? The R4 compressors (1995-older) are pretty notorious for sounding like hell once they start going bad. However, the belt tensioner can go bad and sound very much like a bad A/C compressor. This takes a very careful approach to isolate, since you're working around moving parts. Be VERY careful, please. If you notice when the compressor clutch engages, the belt tensioner oscillating back and forth rapidly, try gently pushing against the body of it with a pry bar, broom handle, etc. anything sturdy that won't slip easily or bend. Not a lot of pressure against it, just enough to stop it from moving so easily. Obviously there's danger in working around the moving belt and other moving accessory drive components, so do this at your own risk... anyway if stopping the tensioner from moving makes the noise go away, you've got a bad tensioner, suggest only replacing it with the OEM style Gates unit. The weird-looking aftermarket ones have been known to act up brand new out of the box.

Richard
My compressor comes on when the a/c is turned off. Not sure if it’s supposed to or not.
 

Kran

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My compressor comes on when the a/c is turned off. Not sure if it’s supposed to or not.

common issue when a transistor goes bad on the hvac control head/box. if the blower fan is off and the AC clutch is still engaged then stuff can freeze over. not good. switch the AC button off when you dont need AC. otherwise if you want to go through the hassle of adding a relay behind the dash to resolve that issue, look at this link. also has other useful info about HVAC controls https://www.silveradosierra.com/how...k-series-trucks-hvac-control-unit-t77522.html
 

df2x4

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My compressor comes on when the a/c is turned off. Not sure if it’s supposed to or not.

Is the selector switch set to defrost? If so that's perfectly normal. The A/C compressor kicks on when the defrost vents are engaged to remove humidity from the air.
 

S1I2F3

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Just throwing this out there...

My AC was recently rebuilt, and was working great, blowing super cold air, with no excessive noise. As the engine would warm up with driving, there wouldn’t be any noticeable audible changes until I would come to stop light - once at idle the compressor was making this insanely loud clicking/knocking sound, to the point that I would turn it to “vent” when stopping since it was so annoying.

Long story short, I got a new belt and that solved the problem (started with the cheapest fix). Logically speaking, as the engine bay would heat up, I suspect the belt would stretch slightly, and there would be enough slack for there to be an inappropriate amount of play in the compressor clutch, inducing the loud clicking. Since the belt tensioner cannot be adjusted, I figured a new tight belt might bring the clutch into spec.

Might be worth a shot!
 

gyver

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Is the selector switch set to defrost? If so that's perfectly normal. The A/C compressor kicks on when the defrost vents are engaged to remove humidity from the air.
Thanks! You are right, it was!
 
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