Only those that don’t know what a search engine is....
A swamp cooler (more formally called an evaporative cooler) is essentially a large box-like frame containing a big fan and walled in by water-wetted pads, usually made of cedar shavings or cellulose. The fan whooshes the hot outside air through the dripping pads (which are continually soaked by a water pump), cooling the air by about 20 ºF as the air evaporates water molecules from the pads. The fan then blows the water-cooled air through the house and out a deliberate vent.
Ah... but it is more complex than that...
I could write a book, Zen and the Art of Swamp Cooler Maintenance.
The fan is ying, the pump is yang... all must be in balance or you will flood your air ducts.
Don’t ask me how I know this.