The thing about window A/C units is that, in my experience, they end up getting disgusting before they end up breaking. If not stored properly they can develop mold and mildew inside the styrofoam "cooler" internals, and that's simply impossible to truly clean because it's not metal or plastic. While wasteful, it's just not worth the respiratory health risk to keep an old machine that can develop some really dangerous molds and spread all over your home.