2004 Nissan Xterra

does it squeal non stop? if so an idler pulley seized up on ya...

Yes it squeals nonstop once it starts squealing. If I turn on the ac when my car is in neutral it don't squeal but when the rpm's come up it starts squealing.
So if the idler pulley is seizing up how do I fix it.

from what you just said, its not an idler pulley... remove your serp belt, and check all the pulleys on the engine.... if one feels like its getting stuck, it may be seizing up when friction builds up.... now it only does this when the a/c is on??? that narrows it down to the compressor clutch...

Yes only when the ac is on. My car has 3 separate belts. The one that goes around the compressor clutch and it's adjuster idler pulley is a new belt and the compressor and clutch is new. I just put it in last night.

3 belts... ok, all are fed from the crank... now is the ac on a seperate belt or is it shared???? normally it shares the alternator... powersteering is probably alone... i believe the waterpump is internal on that, or is it external and fed from another belt??? sorry im a little rusty with these.... back to the ac belt, that has an adjustable tensioner.... how tight are you making the belt??? i understand you just replaced the compressor, but i have seen new stuff out of box no good, so dont rule out that compressor just yet.

3 belts all go around crank shaft. One goes around the alternator, one goes around the fan and power steering and one goes around the ac clutch. Each belt has a tensioner pulley. The belt Around the ac clutch has a little give but it isn't really loose or really tight.

ok. well the ac is the one giving issues, so lets stick with that... new compressor/clutch, was the belt also replaced??? if u reused the old belt, did u mark the direction of rotation? if not, replace the belt, check the adjuster pulley, and tighten as the new belt wears in... this should solve your problem.... keep me posted