Hi pitched whine from AC? on 2003 Dodge Ram Van 3500

I hear a hi pitched whine when I accelerate WITH THE AIR CONDITIONING ON, then rises in pitch and fades in volume.
It stops when I turn AC off. What are the most likely culprits?

Thanks a million

Asked by for the 2003 Dodge Ram Van 3500
This sounds to me like it may be a worn belt. That's be the first thing to check.