Mounting a Standard Air Conditioner in a Sliding Window (From the Inside, Without a Bracket)

Step 3: Starting the Frame

Lay a shorter piece of 2X4 down and screw the ends of the longer pieces to the ends of this shorter one, as shown. Because of the depth of the lumber, I used deck screws, 2 at each connection point.

Create a rectangle by screwing another short piece of 2X4 between the long pieces at the other end, as shown. Make sure the corners are square.

At this point, it's a wise idea to put this rectangle into the window opening to make sure it fits. It should slide in and sit against the window framing. (If it's a little loose, you can use shims to help wedge it in place during installation.)