A system for providing a comfortable environment within the passenger compartment of a vehicle. Controlled ventilation is utilized, along with a heater, an air conditioner, or an integrated heater and air-conditioner system. Linked to the setup is a windshield defrosting and defogging system capable of clearing the windshield. Some vehicles have a ventilation-air filter which cleans the outside air that enters the passenger compartment through the fresh-air inlet. The increasing glass area of many passenger vehicles places an additional load on the air conditioner. Many vehicles incorporate solar-control glass to reduce solar transmission to the interior.
Heating
There are two types of passenger-compartment heaters: engine-dependent and engine-independent. The engine-dependent heater utilizes waste heat from the engine. The engine-independent heater includes a small combustion chamber in which fuel is burned.
Most vehicles have a liquid-cooled engine and an engine-dependent heater through which hot engine coolant flows. The coolant passes through the tubes of a tube-and-fin heater core (see illustration) while air flows between the fins. Heat output into the passenger compartment is regulated by controlling either the coolant flow or the airflow. An electric blower motor may run at various speeds to help move the air. When the heater is turned off, a coolant flow-control valve may close to stop the flow of coolant through the heater core. See Dewar flask, Engine cooling
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Air conditioning
When the outside temperature is above 68°F (20°C), the passenger compartment may be uncomfortable for the occupants unless the inside air is cooled. Cooling is provided by a mobile, vehicle-mounted refrigeration system known as an automotive air conditioner. The automotive air conditioner combines the refrigeration system with an air-distribution system and a temperature-control system to cool, clean, dry, and circulate passenger-compartment air. Cooling is provided by a mechanical vapor-compression refrigeration system with five major components: compressor, condenser, refrigerant flow-control valve, evaporator, and a receiver or accumulator that includes a desiccant. See Compressor, Evaporator, Heat exchanger, Refrigeration
Operation, air temperature, and air distribution through the passenger compartment may be controlled either automatically or manually by the driver. In some vehicles, conditioned air distribution can be controlled for each seat or seating position. See Air conditioning
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