So my car has been making a low whirring noise for a little while now. My alternator busted a week ago, and I thought that when I replaced it the noise would go away, assuming the noise was coming from a worn out bearing or something. No such luck.

I started the car without the alternator belt, and the noise didn't go away.

I removed the belt for the AC pump and the noise was gone.

Now for the tricky part...how do I figure out if the noise was coming from the AC pump or the tensioner pulley? I can't run one without the other?

I did spin the tensioner pulley and it made some noise...should it be absolutely silent like my new alternator is?

A drawing for your reference.

sounds like either the tensioner is fucked or both the tensioner and AC compressor is fucked. try replacing both.

^Ya I figured that, but I'm not too keen on replacing the AC compressor...since I'm sure they run a few hundred bucks and involve re-gassing the system.

I could just replace the tensioner pulley I guess...see if that solves it.

For now I'm just running sans belt...just to get rid of the noise.

Have you run the A/C recently? I've read that it's good practice to turn on the compressor regularly to cycle the lubricant contained in the lines. Mine comes on with the defrost function so even during the winter it gets used.

If you're going to start throwing parts at it definitely start with the tensioner since it will most likely be less expensive and far easier to replace.

^hum...come to think of it, I don't remember if the sound was there last time I ran the AC. That might be a good place to start.

Yea, it could be something with the AC clutch being disengaged

How about asking this question on nasioc?

I think I know of the noise you speak. I started hearing it in my work truck and it lasted for about 3 months...then the AC compressor took a complete shit. Far different cars but I'd imagine the workings of an AC unit wouldn't vary all that much between makes for the most part.

I haven't been running the AC compressor for the past few days, and wow.

The engine revs so much smother, blipping the throttle for down-shifts is so sweet. I'm not experienced enough to try and put a figure on the amount of power I have gained, but I'm really tempted to just leave the belt off.

We'll see how my resolve stacks up when it's 35 degrees c.

Are you comparing it to having the belt on and the A/C on or the A/C off? If the A/C is turned off, there should be very little difference.

I have been running it without the belt, and there is definitely a difference...which might be expected if something were wrong with my pulley or compressor...like if there was something wrong with the bearings.