Re Question..
The device on the roof you describe is not a swamp cooler, But rather a water tower, Air Conditioning uses to use water instead of the now common condenser or outdoor unit, the water condenser worked like this, when the ac compressor was running, the water circulated around the condenser coild, thus absorbing the heat from the freon, then the hot water was pumped to the roof, and sprayed over the wooden slats, thus cooling the water, it was then pumped back to the condenser in the basement, this system was very efficient, but much more complex, thus they went away in the 1960s, maintenence on them was expensive, and as some of the water evaporates, water must be added along and along, water costs rose so now about all you see is the regular fan condensers...the water ones are much more efficient and produce ice cold air because water is a much better medium to absorb heat!The antique mall in my hometown is in the building that was Shields Hardware for many years, they were a Carrier dealer, and their is still one of these units being used today! it was installed in the early 50s and has a cast iron compressor and uses I think Freon 502.." maybe 500??" in any event, if you stand in front of it, its so cold it will make your teeth hurt!!