99 cherokee squeaking

Does anyone have an idea why my engine is squeaking, here is what happened. Today I replaced the serpatine belt and when I turned on the car there was no squeaking but when I turned on the ac/def I had a horrible squeaking sound. I am hoping it is just because I didn't tighten the belt enough. I am going to try to tighten it more tomorrow. I was wondering if anyone else has an idea of what it could be. Thanks

Your AC compressor may be seized.

The 'horrible squeaking sound' may be the AC compressor clutch slipping.

In this case, tightening the belt would not help, and you need a new compressor.

I would try tighten the belt first. Mine squeaks a little at times when cold. Make sure the idler pulley bearing is good too. AC compressor is easy to check, open the hood and see if it is turning.