On many homes I inspect I come across old evaporative coolers that haven’t been used in a long time. New generation heat pumps and other more efficient methods of heating to cooling have rendered that older technology somewhat obsolete. The engineering on old evaporative coolers is still usable for several months out of the year but the homeowners usually tend to forget about them. It’s a classic case of out of sight, out of mind. The issue lies in that there may still be a water line running to them. Over time they tend to leak and this can produce problems up on your roof and especially to the wood underlayment that surrounds the unit.
It may be somewhat difficult to see from this picture but the sheathing or plywood that is directly nailed to the trusses on your home can incur damage over a period of time from that leaking old evaporative water. This photo shows the white and ashy greying of the wood as water keeps moving across it. The slow water movement can damage and warp wood. It can also cause mold and a general weakening of the roof in that area.
I always walk the roof of the homes I inspect and I can always feel the “softening” or give on a roof where old evaporative coolers have done their damage to the roof, whether the unit is still there or not. It doesn’t mean that that has to be repaired right away but the source of water must be stopped, the old evaporative cooler be made inert and the roof repaired in time. I always point this out to clients interested in buying the home because it will have to be taken care of, either before or after the sale. If the roof covering is old anyway, it may be time to replace the shingles and replace that, and any other boards that need to be removed before a new covering be placed into position. The main issue is that the possible new home buyer be informed.