How does an Air conditioner work? Also, what are the most efficient types for cooling?
The basic principle of operation is that a refrigerant (such as Freon) changes state from a gas to a liquid and back again.  It absorbs heat in one phase and gives off heat in another.  In an air conditioning system it is pumped through coils which absorb or reject heat depending on their orientation with respect to the flow of the refrigerant.