I think by "air cooler" you're referring to what is commonly referred to as a "swamp cooler." They cool the air by blowing it over water, which due to water's high capacity for heat and how much energy it takes to evaporate water, cools the air significantly. These are much more economical than air conditioners, which use a compressor and cool air by blowing it across coils in which decompressing gas causes them to become very cold. The downside is swamp coolers add a lot of humidity to the air, so unless you live in a very arid place, like Utah, you're going to end up with a very humid home. That's why you don't really find them in states that get both hot and humid, which is where air conditioners are the most prevalent because they actually remove humidity from the air.