Air conditioning refers to the cooling and dehumidification of indoor air for thermal comfort. In a broader sense, the term can refer to any form of cooling, heating, ventilation or disinfection that modifies the condition of air. An air conditioner (often referred to as AC or air con.) is an appliance, system, or mechanism designed to stabilise the air temperature and humidity within an area (used for cooling as well as heating depending on the air properties at a given time), typically using a refrigeration cycle but sometimes using evaporation, commonly for comfort cooling in buildings and motor vehicles.
The concept of air conditioning is known to have been applied in Ancient Rome, where aqueduct water was circulated through the walls of certain houses to cool them. Similar techniques in medieval Persia involved the use of cisterns and wind towers to cool buildings during the hot season. Modern air conditioning emerged from advances in chemistry during the 19th century, and the first large-scale electrical air conditioning was invented and used in 1902 by Willis Haviland Carrier.

Car air conditioner systems are designed to allow the driver and or passengers to feel more comfortable during uncomfortably warm humid or hot trips in a vehicle. Cars in hot climates often are fitted with air conditioning. There has been much debate and discussion on what the usage of an air conditioner does to the gas mileage of a vehicle. Factors such as wind resistance aerodynamics and engine power and weight have to be factored into finding the true variance between using the air conditioning system and not using it when figuring out difference in actual gas mileage. Other factors on the impact on the engine and an overall engine heat increase can have an impact on the cooling system of the vehicle.

The Packard Motor Car Company was the first automobile manufacturer to build air conditioners into its cars, beginning in 1939.These air conditioners were originally optional, and could be installed for an extra $274 ($4176.08 in 2009 US dollars), though they took up the entire trunk space and were not very efficient. General Motors introduced a more efficient air conditioner beginning with its 1954 Pontiac V8 models, but automobile air conditioners would not become truly commonplace until the 1970s and 1980s.

Most car air conditioning systems use compressors that are engine driven, which cannot be used in hybrid and electric vehicle applications. Electrically powered air conditioned systems have been used on electric vehicle