Swamp coolers only work in dry climates, and only when it's not too hot outside. People stopped using them in Phoenix because they really don't work that well

Swamp coolers only work in dry climates, and only when it's not too hot outside. People stopped using them in Phoenix because they really don't work that well in the middle of the summer now. They can also cause mold problems. Some houses will have "piggyback" systems, with both a swamp cooler and regular A/C, so they can switch to the A/C when it's too hot for the swamp cooler, but modern A/C units are so efficient it's probably not that cost-effective to do that any more.