How it works in a nutshell: First you put a refrigerant gas into a sealed system. This refrigerant is then pressurized using a compressor. As it's pressurized, it gets hot by absorbing the heat around it. This hot gas is then circulated through a series of tubes that dissipate the heat. Scientifically (and more correctly stated), the gas removes heat rather than adds cold. The gas can lose lots of its heat – in other words it gets really cold when you reduce the pressure. As it cools, it becomes a liquid. This is when you get cold air blowing on you. To use this system in a car, it needed very little adaptation from its early applications as a building refrigeration device. The basic components found in automotive air conditioners are the refrigerant gas, the compressor, condenser, evaporator, accumulator and expansion valve. Depending on the car make and model, there might be an orifice tube or receiver-drier. All these components have a specific task, so let’s look more closely at each one.  
Typical automotive air conditioning system and components.