Abstract: A dispensing system for dispensing a deodorizing, disinfecting or freshening substance is mounted in the heating and air conditioning ductwork of a vehicle, and includes an electronic controller that controls the operation of the system. The substance dispensed by the system is spread through the ductwork throughout the interior of the vehicle by the heating and air conditioning system of the vehicle. The system is operated during a cycle that includes an ON time, during which the substance is dispensed, and an OFF time, during which the substance is not dispensed. The system is configured to cycle only when the vehicle ignition is on. The system can also be configured to cycle only when the parking brake is released, or when the vehicle transmission is in gear.