As I was sitting in my 15 year old car with a broken AC on the way home from work yesterday I decided this would be a good idea. I am only going to explain evaporative coolers in this post, there is another type called an absorption chiller but it is more complicated and although I understand it I am still trying to figure out how I'd like to explain in here in stuff I don't understand.
Evaporative Coolers -
Evaporative coolers draw outside air in and pass the air through a wet pad such as a water soaked sponge. In doing this some of the sensible heat is converted to latent heat by evaporation of water of of the wet pad. Although the total heat (sensible heat + latent heat) remains unchanged if the entering air is dry enough it can have substantial effects.
Sensible Heat - Potential energy in the form of thermal energy (heat). It is heat that is added or removed from air without a change in water vapor content.
Latent Heat - The amount of energy released or absorbed during a change of state or phase transition.
Phase Transition - The transition of a substance from soild, liquid, gas or plasma to another phase of matter.