AC or AC pulley whine, or something else?

[ryanougrad]

Sorry if this is long trying to be as detailed as possible. I have a 2000 LX470 with 119k. When running my AC my truck idles at roughly 700rpm while in drive. At this RPM I get a small whine that I can hear in the cabin. The minute I accelerate the sound, as far as I can tell goes away. Also cannot hear the sound when driving.

I played around with the idle a bit today and if I have the AC on and put my truck in neutral the RPM's go to 800. At 800rpm, even with AC on I have no whine. Also, on occasion, I idle at 600rpm, again no whine with AC on. I assume the 600rpm idle is when the compressor isn't active and my truck is just blowing air, as I can see the RPM's change and feel a kick of the compressor when it goes back to 700rpm.

So, anyone have an idea of why my truck has this whine only at 700rpm with the AC on? To be clear, AC off equals no whine and truck idles at 600rpm in drive. My current guess is pulley bearings, but could be wrong.

 

[badlander]

I get the same type of sound when idling with the ac on. Been that way since I bought it years ago. AC still works fine. I believe it has something to do with the fluid or gas passing thru the tubes when running. I even had it checked out by an AC place as I was also concerned right about the sound. They said it was normal and not to worry about it.....
Hope that helps.

 

[Sandroad]

My AC is whiny at idle too. I'll check the fluid for bubbles today. If that's ok and the whine stays the same, I'll ignore it.

 

[ozmanyyy]

Mine does this too. It started sometime a year or so ago. I had it checked out and besides the noise, it works fine.

Though I wouldn't say its normal. I had the truck for a few years and like I said, this started sometime last year.

 

[ryanougrad]

Hum. I'm all for preventative maintenance and if I can figure out the fix I will. But I don't want to throw money down a rabbit hole either.

 

[MattThompson]

Anyone ever find a fix for this? Mine started doing the same a couple weeks ago.

 

[hardhat]

Mine was whining a little, turned out to be the alternator.

 

[ozmanyyy]

No change on mine. The whine happens whenever the AC kicks in. Easy enough to check, hit the AC button when you hear the whine and it goes away when you turn it off. I have noticed, recently, when it's really hot, the AC light flashes. I have to click it off and on for it to kick back in. Other than that, it works.

Oz

 

[MattThompson]

Mine was whining a little, turned out to be the alternator.

My mechanic said it may have been the alternator even though the sound appears to have gone away.

 

[MattThompson]

No change on mine. The whine happens whenever the AC kicks in. Easy enough to check, hit the AC button when you hear the whine and it goes away when you turn it off. I have noticed, recently, when it's really hot, the AC light flashes. I have to click it off and on for it to kick back in. Other than that, it works.

Oz

After dealing with my AC compressor clutch and pulley bearing recently, what you are describing sounds like the clutch is slipping and kicking the AC off. My light on the button would flash and it would start blowing hot air and only turn back on after i turned it off and back on. I was panicked thinking something major was wrong and living in OKC with 100 degree plus weather, I went ahead and had the clutch and bearing replaced.

 

[ozmanyyy]

After dealing with my AC compressor clutch and pulley bearing recently, what you are describing sounds like the clutch is slipping and kicking the AC off. My light on the button would flash and it would start blowing hot air and only turn back on after i turned it off and back on. I was panicked thinking something major was wrong and living in OKC with 100 degree plus weather, I went ahead and had the clutch and bearing replaced.

Very possible. But my AC still blows ice cold and it's been like this for over 2 years now. I'm not throwing more money at it unless it actually breaks.

Oz

 

[Somebodyelse5]

My mechanic said it may have been the alternator even though the sound appears to have gone away.

I put in a new alternator, whine still exists, definitely something with the AC system as it is dependent on whether the compressor is on or not

 

[BillZ260]

@ 140K my 02 LX is making this sound too, glad it's probably not the alternator.