To improve driver and passenger safety a supply of fresh air is necessary to reduce fatigue and maintain comfort.
Fresh air is drawn from outside usually through ducts at the base of the windscreen, and directed to the passenger compartment.
The air is then delivered through ducts and flaps which are positioned to direct air to particular points inside the passenger compartment.
These flaps can be controlled by cables, by vacuum servos, or by electric servos.
In this way air can be directed to the face ducts, floor ducts, window demisting ducts, and rear passenger compartment ducts.
A fan driven by an electric motor is used to assist the air to flow through the passenger compartment when demands are high or when vehicle speeds are low.
In internal combustion engines much of the heat generated is lost to the atmosphere or wasted. Some of this heat can be used to heat the incoming air to a comfortable level when required by the vehicle occupants. Engines that are liquid cooled direct heated coolant to a heater core to heat the air.
The heater core is a small radiator consisting of tubes, fins and tanks. It is mounted under the dash panel inside the air plenum chamber where air can be passed across the core fins and into the vehicle interior. The heater core is connected to the engine’s cooling system by flexible rubber hoses which allow for movement, and a reduction in the level of engine noise and vibration transmitted into the passenger compartment.
The rubber hoses are fabric reinforced to resist cooling system pressure and temperature.
The coolant flow is created by the engine water pump, directing the coolant through the heater core and then back to the engine.
A heat control valve is located in one of the heater coolant hoses to adjust the quantity of coolant flowing through the heater core.
The valve can be operated by a cable and lever system. A lever mounted on the vehicle’s dash panel is connected by a cable to another lever on the heater valve. Movement of the dash lever is transferred through the cable to the lever on the heater valve.
With the dash lever in the maximum heat position, the valve is fully open allowing the maximum amount of coolant to circulate through the heater core.
When the engine is at normal operating temperature, some of the heat in the heater fins is transferred to the air passing over them. The heated air can then be directed to raise the temperature in the passenger compartment.
Moving the lever to obtain a cooler temperature setting reduces the valve opening. This restricts the amount of coolant flowing through the heater core. Less heat is then transferred to the air passing over the heater core fins.