Not sure about your gas levels... mine only started the hissing after I topped it up... unless we both have major leaks that would imply your levels are ok???

I have read in other places that the hissing is normal and is the liquid turning back into a gas when the air con is shut off.

I think only the centre vents are cooled so make sure they are open (not the outside ones).

Don't know about the pulley but it wouldn't surprise me... the belt arrangement at the front is tricky and looks difficult to maintain (so probably isn't).