It looks to me like the one unit is an evaporative cooler that's on its way to the dumpster, having been replaced by the AC unit behind it. Is the "swamp cooler" even connected, or was this just a convenient place to store it?
FWIW: Some years ago, I visited East Berlin. I noticed many multi-story buildings, damaged in the war, had accumulated so much grit on their roofs that trees had taken root. So, it's conceivable that someone might find this on a rooftop some day.