I was referring to the panel outside. There is a ground bus bar that wires can be attached to. Usually many open spaces, takes a flat head usually. Knock outs on the box allow additional access. You can add conduit if you are anal or just run the wire out to a rod with a ground lug. You may have one already. Check for corrosion if existing is present. You could facilitate the existing ground wire from elect outlet by adding a jumper out to ground lug on unit.I didn't want to drill another hole in my wall of my house.
Probably won't.