The water from rain helps the heat dissipate from the outside radiator on central A/C systems, according to an article I read. https://www.integrityair.com/is-my-air-conditioner-performance-affected-by-rain/
It makes sense, it evaporates out a lot of heat so the overall system is more efficient.
So why are air conditioners not designed to have a water hose to lightly spray on it all the time? Wouldn't this improve efficiency enough to offset the cost of the water spray?