An air conditioning system that can operate an air conditioner of an electric vehicle without interfering with the charging process, which utilizes a secondary battery. When operation of the vehicle is terminated and the control system determines that a frosting judgment decision is positive, the control system judges whether the charging current has dropped to a specified level or less. As soon as the charging current has dropped to or below the specified level, the excess charging current may be used for a defrosting operation. When the operation of the vehicle is stopped and the control system determines that a frosting judgment decision is negative, the control system judges whether a preliminary air conditioning switch is on. If the preliminary air conditioning switch is on, it is judged whether charging of the secondary battery is in progress. If charging is progressing, the control system determines whether the charging current has dropped to or below a specified level. As soon as the charging current has dropped to or below this specified level, preliminary air conditioning is performed to cool or warm the cabin of the vehicle during charging of the secondary battery.