While it’s true that Maintenance is Underappreciated, I think maintained is itself a form of appreciation. If you’re maintaining a thing, you’re aware of it, and putting in the effort to maintain the value it brings. If you set-it-and-forget-it, it literally is out of sight, out of mind, and not appreciated.
If you want to be appreciative that the air conditioner is doing its job, change its filter. Mowing the grass is a great way to appreciate that you have grass to mow.