To install an air conditioner in a double-hung window, lift the unit into the window, align the bottom flange with the outside edge of the sill, and then close the window. Instructions vary depending on the parts included in the kit, such as mounting brackets and weather stripping.
A standard window air conditioner installed in a double-hung window does not typically require a kit or any additional accessories, although a heavy unit may require a metal bracket to help support the weight. Any support bracket should be level with the window sill and attached to the frame.
Before installing the air conditioner, attach the curtains to both sides of the unit. With a helper, lift the air conditioning unit into the window. Align the bottom flange of the air conditioner with the outside edge of the window sill, and then close the window so that it rests on the top flange of the unit. If a bracket is installed, the air conditioner should snap firmly into place. Spread open the plastic accordion curtains on either side of the air conditioner, and screw them to the window frame.
The installation kit may also include weather stripping and L-shaped brackets, which prevent the window from being forced open. Fit the weather stripping in the gaps between the window pane and the lower window sash. If provided, secure the L-shaped brackets to the top and bottom sash frames.