The installation of a through-the-wall AC unit may present a challenge for those who have not had previous carpentry experience. If you have the carpentry skills, gather your materials: AC wall unit, circular saw, router, nails, hammer, caulk, tape measure, pencil, two pieces of 2-by-4 lumber, stud finder, level, utility knife, power drill, screwdriver, socket set, safety goggles, hand saw, miter box, and molding and finishing nails.
Prepare the area
Move any furniture or decorations out of the way, and remove any pictures or paintings from the wall.
Locate the studs in the wall
Use a stud finder to locate the proximity of studs in the wall and mark them so that you know where to cut only one stud.
Cut the insulation
Use a router to cut through the interior wall along the outline after measuring the dimensions of the unit. You may then cut away the insulation with the utility knife.
Make the necessary wall holes
Use a power drill to bore through the outside wall at each of the four corners from the inside, but use the holes drilled to stencil an outline on the wall on the outside. Cut through the exterior wall along the outline with the circular saw, but use the hand saw to cut through any 2-by-4s blocking the hole.
Level the unit
Use the level to make sure the 2-by-4 fits on top of the cut vertical wall studs at the bottom of the hole. Drive a nail down through the 2-by-4 into the cut vertical studs. Repeat this step with another 2-by-4 at the top of the hole.
Mount the bracket
Mount the AC bracket into the wall using the manufacturer's supplied hardware, and use the level to make sure it balances before securing.
Install the unit
Slide the AC unit into the hole, and secure it to the bracket using the manufacturer's supplied hardware after applying caulk to the outside bracket. Use more caulk between the outside of the unit and the exterior shingles or clapboards.
Secure the unit
Secure the unit by using a handsaw and miter box to cut appropriate-length molding at 45-degree angles. Place nail screws around the unit.