AC Noise: Please help with diagnosis

[Ironhead]

98 RCLB, 5.7 Vortec, all stock. 90,000 miles.

The issue is a noise, kinda like a slipping belt, only happens when the AC is on. Belt is new. Hard to discribe the noise, but it is a bit like a slipping belt, a bit like a whistle, or escaping steam. Only happens when AC is on, and most noticeable when stepping on the gas after engine at very low revs, like under 1000.

Is this normal for these trucks? Anybody else experience this? If so, got any idea of whether there is something wrong, or whether I'm just being too fussy.

Thanks in advance guys.

 

[Fuzzy]

Not normal, Compressor could be seized causing the belt to slip on the pulley, if it's been doing it for a while I would pull the belt off and inspect that and the groves on the AC Compressor pulley for rubber.

 

[df2x4]

Level of noise from the compressor while it's running varies from truck to truck in my experience. Kind of hard to tell without actually hearing it, but you probably shouldn't be hearing a whistling noise...

 

[Ironhead]

I will most definitely check the belt/compressor pulley as advised. I should have added that the AC blows nice and cold, and that this started after the belt was changed. I'm inclined to go to a GM dealer and get an OEM belt, after I do the checks. The tensioner seems fine, and the idler pulley runs free.

Under a heavy load (AC on full, headlights on) the alternator pulley gets hotter than I think would be normal, which may indicate that the belt is slipping.

What's the best way to clean the grooved pulleys? Is brakecleen ok to use?

 

[Ironhead]

Thinking that it's kind of crazy to ask the forum to help diagnose a noise that they can't hear, I drove the beast over to a buddy's place the other day so he could listen. We both came to the conclusion that the noise comes from the AC compressor pulley area, and only when the compressor is engaged, and the engine rpms are over 1000.

With that in mind, I remember that we had some trouble sourcing the correct serpentine belt at the parts shop (NAPA). Decided to order an OEM replacement from a GM dealer, and will install it on Tuesday to see if that fixes the problem.

In the meantime, is there any proper way to clean the various pulleys that the belt rides on? Something that does not leave a residue or do anything to cause slippage.

 

[Ironhead]

Diagnosis done and problem solved: it was a serpentine belt a bit too long, chirping or screeching under load. Solution, got two more belts, and fitted the shortest of the three, and the noise is gone, plus there is still some movement in the tensioner.