ac in wall
Yes you can do that with a room AC into the wall(that is how our add on family room is done). If youare handy with electricity you can also hard wire it into the electrical system of the house (drawback is unwiring it if it needs a repair). You an either leave it there year round with a cover over it on the outside for insulation in the winter or pull it and have a drop in "door" that you insert from the outside (to handle the rain in the wall issue) with a seal and fasten on the inside to keep crooks out. Carolyn