that sounds like the answerif the smell only occurs when a/c is turned on then the problem is that the a/c pump is very hard to turn or stuck.
when a/c is off the pulley still spins but doesn't engage the pump.
turning it on, i believe engages a magnetic clutch in the pulley and therefore turns (or tries to ) the pump.
the noise is the belt sliding on the pulley instead of freely turning with it. same as the smoke is due to the friction of belt sliding along pulley.
another possibility is the belt and/or the tensioner are faulty. allowing the belt to slide instead of gripping when extra load of a/c pump is engaged.