To install a window air conditioner, open the sash fully, slide the unit into place and close the sash. Extend the unit's curtain and use screws to secure the sash to the unit and hold them in place. Plug the unit into an appropriate power outlet, and start the cooling.
Install the unit so it is level from front to back. Manufacturers create channels in the bottom of the unit to facilitate drainage without tipping. Avoid tipping the air conditioner forward to prevent the water from spilling inside the home. If you prefer to avoid drilling holes for screws to secure the unit to the sash, place thin wood strips, cut to size between the top of the sash and top of the window to prevent accidentally opening it.
Installing the window unit keeps the sash open and leaves a gap between the top and bottom windowpanes. Many manufacturers provide foam weather stripping material to insert between the panes. This material keeps insects and dust out of the house.
In homes with vinyl windows, the air conditioner may be too heavy for the window to support. One solution is to install a shelf under the window using L-brackets and a board. This support prevents damage to the window and potential damage to the air conditioner.