A cooler on the roof is the appliance your tenants were never taught to use
Much of the older stock here cools with an evaporative unit, and it only works if the person living under it understands what they are operating.
A swamp cooler pulls outside air through wet pads, which is why it works at all in air this dry and why it stops working on a humid August afternoon. A tenant raised on refrigerated air closes every window, wonders why the house is damp and warm, and reports the unit as broken.
The calendar has hard edges. The cooler is started in spring and drained before the first hard freeze, and a line left with water in it through a Denver winter splits somewhere expensive.
The whole thing sits on a roof. A tenant cannot look at it, a handyman with a ladder is not always the right answer, and every question about it lands on your office instead of being solved in the driveway.
So put the equipment on camera. The pads, the water line, the belt, the damper on the duct, the bleed valve. An owner in Lakewood watching a pad change understands the line item, and a tenant in Aurora watching the same clip stops calling in May.