How to safely install a window AC unit?
Measure from the top of the bottom sash to the top of the window casing. Get two pieces of wood about 2" by 2" and long enough to reach from the sash to the top of the casing. Cut them long enough to be a tight fit. With the wood wedged in the a/c unit should be secure. This also works on first floor units where added security is a factor as the window cannot be easily opened from the outside.