Automotive AC systems are very straight forward in their purpose. That purpose is to cool the air that is moving through the cabin of a vehicle. This result is achieved by blowing the air entering the cabin over a cooled surface (evaporator) which transfers the heat from the air to the coolant liquid that is flowing through the unit.

The process begins with the pumping of a mixture of specialized oil and Freon through the system. The compressor is the unit responsible for creating this movement, after the fluid leaves the compressor is passed through the filter (Drier) and any debris that is suspended in the mixture will be captured.  Now the compressed fluid (which carries a lot of heat) is passed through the condenser which is a unit that expands the fluid so that there is as much surface area  where air can pass by. The passing air will pull the excess heat out of the fluid and cool it so it can perform its job. Next the fluid passes through the expansion device where the lines that carry the fluid expand, this allows the fluid to cool even further. Finally the fluid now travels through the evaporator where the heat from the air is absorbed again and the whole process starts over.

The ability of the system to cool is very dependent on the temperature of the air around the system and can give varying results in times of extreme heat. Needless to say that on a 100 degree day the cooling will not be as effective as on a cooler day.