So I just removed a wall A/C unit in my house, which was built in 1949. First time I've ever seen a cross section of my house's construction. My walls from face to face are 11.5" thick. Solid brick, concrete block, inside 2x framing and gypsum board with plaster. Guess the people who built this house wanted it to last for a while.
I'll be putting a stained glass window in the spot. No wonder the central A/C guys that put my system in this past Spring were bitching and moaning when they were drilling through the walls.