My dad's 1998 Dodge Caravan makes a horrible screaming noise when running the A/C. It's so awful I have to turn it off.
The noise doesn't start immediately. The A/C can run for several minutes, before it starts to squeal. It gets worse when accelerating.
I have replaced all the belts already. Someone told me the compressor is bad. However, the air gets ice cold, so the compressor obviously works. What could be causing this?

The problem may not be the actual compressor, but the drive pulley that is on the front. If the bearing on that pulley is failing, the condition becomes more noticeable when it is allowed to heat up, like during operation. Does the noise occur only when the A/C is run?

Find someone who can diagnose this and possible replace just the pulley, clutch and coil.

You may need to replace the entire compressor, but only if the compressor is the component that actually failed or has been damaged by the failed pulley.

So far, the noise occurs only when the A/C is running. Like I said, the air gets cold, so I think the compressor is doing what it's supposed to do. I will try to find a shop that will check into what you've told me. Thanks for your help... Wish me luck.

Look at the belt yourself... find the longest span and push. Does the tension seem "weak"?
You can take your vehicle to a shop and simply ask for a second opinion about the belt and the belt tensioner. The should be able to explain in simple terms exactly what your vehicle needs. Let us know...
Goodluck, G2K!