Lick the underside of your wrist and then blow on it---it will feel cool even though your breath is over 90 degrees. Evaporation absorbs heat. The cooler has water in it and a mesh to hold the water and let air pass through it, where evaporation occurs, and then comes into the car as cooler air. A swamp cooler will work fairly good (cool air, not cold) in the desert Southwest or in other low humidity areas where evaporation is rapid but not at all well in high humidity areas. Used to see cars with the window cooler and a canvas water bag hung on the front bumper where the water evaporating from the damp surface cooled the water inside (slightly). Bag could also be used to top off an overheating radiator. Old enough to have lived through it.
