My question is why is the A/C engaging with the A/C off? Is it broken? If you want to disable it by cutting the belt but you may end up disabling other units that run off that belt. If I stand corrected the A/C pulley spins freely until it is engaged by turning the A/C on at which point a load is added. So the belt already runs through and by the A/C pulley, so cutting it is most likely going to disable other things the belt is associated with in addtion to the A/C unit.