A/C "moan" 1989 K1500. 350 tbi.

[Arkansas89Chevy]

Recently put new AC compressor, drier, expansion valve, o-rings, pressure switch, etc. on the truck. Best I can describe the noise is a "moan" under the hood at a very specific rpm ONLY when the AC is running. Truck does not have a tach, but it happens around 25 mph, and is worse when i'm coasting. I can slightly press the gas pedal to make it go away. It's almost like something is vibrating under the hood at a certain rpm/frequency. I've checked for loose brackets, etc. till i'm blue in the face. And it's odd that it only does it when running the AC. Anyone experienced this or have any ideas?

 

[PlayingWithTBI]

Anyone experienced this or have any ideas?

Yeah, my compressor (in my 88) does it when at idle, in gear, at ~750 RPM. If I put it in neutral and rev it up over 900 it'll go away. And this R4 is a genuine ACDELCO made in the US of A

 

[1998_K1500_Sub]

Recently put new AC compressor... Best I can describe the noise is a "moan" under the hood at a very specific rpm ONLY when the AC is running.

I believe on that truck there's a bracket (really a "rod") that bolts to the back of the compressor and to the intake manifold to provide stiffness / support. There might be another, similar "rod" from the compressor's mounting bracket to the water pump. Do you have something similar?

My 1995 S10 V6 4.3L had both on its R4 compressor IIRC.

 

[Arkansas89Chevy]

I believe on that truck there's a bracket (really a "rod") that bolts to the back of the compressor and to the intake manifold to provide stiffness / support. There might be another, similar "rod" from the compressor's mounting bracket to the water pump. Do you have something similar?

My 1995 S10 V6 4.3L had both on its R4 compressor IIRC.

It's just got that one rod at the top, going to the manifold, and it's tight. Thanks though. It's driving me crazy! Ha ha

 

[PlayingWithTBI]

I believe on that truck there's a bracket (really a "rod") that bolts to the back of the compressor and to the intake manifold to provide stiffness / support. There might be another, similar "rod" from the compressor's mounting bracket to the water pump. Do you have something similar?

Yeah, mine has the rod for the compressor and a rod going from the T-Stat housing to the bracket but, mine still whines too.

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[1998_K1500_Sub]

It's just got that one rod at the top, going to the manifold, and it's tight. Thanks though. It's driving me crazy! Ha ha

Are you getting some moan from an idler / alternator bearing that’s carrying more load on the pulley when the compressor is running?

 

[Arkansas89Chevy]

Possibly, but i dont think thats the case because it only does it at a very specific speed/rpm. I can literally almost rest my foot on the gas pedal when it starts moaning, and it goes away.

 

[1998_K1500_Sub]

Possibly, but i dont think thats the case because it only does it at a very specific speed/rpm. I can literally almost rest my foot on the gas pedal when it starts moaning, and it goes away.

Do you have a mechanic’s stethoscope? They are handy for things like this…

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[Arkansas89Chevy]

Do you have a mechanic’s stethoscope? They are handy for things like this…

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No, but i need to get one.

 

[slovcan]

I am getting a similar noise. I have replaced the idler pully, tensioner and pulley, alternator a couple of years ago and compressor just in the past month. It happens even when the A/C is not on. It is intermittent and has been for several years. I notice at idle when just started for a minute, maybe. Having just had the A/C system (all new) just charged I now hear it for longer sometimes. Today when it "spooled down" after engine shut down, I figured out what it is. Would you like to know?

















Ahhh, OK. It is the fan clutch.

Cheers,
Glenn