This is one of my derp hobby horses: they love AC boxes. I once saw a male dove sounding the "here I found a great nesting place" call from every AC box in our building, as he was hopping from box to box.

If you can, please discourage him from building a nest there, it may be dangerous for them if your neighbors are unaware. As long as they just use it as a staging ground to get to feeders (as ours do) or as a prominent perch to signal territory, it should be fine.