What a blunder on my part ! I should have asked that question before anything else.
If the vehicle was driven any considerable distance where it could have overheated presents a whole new set of possibilities. If it didn't overheat One of the things that could be done is ; disconnect the belt and turn each individual pulley the belt drives and feel for any roughness or noise. Neither of those two should be present so the pulley with the problem would most likely need to be replaced. Keep in mind that when the A/C or defrosters are on the A/C compressor is working and if there is a problem with it , it would be best to unplug the plug to the compressor clutch to prevent it from locking up and possibly throwing off the belt.