I installed the TuneRS UD pulley to my 2.5L a few years ago.
I never noticed any differences between AC on or off before or after the install, but with the UD pulley I'd like to say the engine feels like it has a bit more torque available at lower rpms.
However if you order one you should keep your expectations in check.
Does the whine you are talking about sound like
this?
If yes then more than likely it's the timing chains, especially the older roller IMS chain if I've understood correctly.
For me it's the worst between 1800-2100 rpm driving at a steady speed and there's not much you can do.