Abstract: A system for providing a supply of air to the passenger compartment of a vehicle, the system comprising ducting for supplying air to a vehicle passenger compartment, a blower for propelling air through the ducting, a heat supply for supplying heat to the air, an evaporator for cooling the air, a vehicle speed detector, and a control unit for controlling the speed of the blower, and an engine sensor which produces a signal indicative of whether the vehicle engine is running, wherein the control unit is arranged to limit the blower speed to a predetermined level if the blower has been operating for a predetermined period while the vehicle speed is below a predetermined level, and to control the system in various other ways.