This is the most common method and works best for the standard "accordion" side panels that come with most AC units.
A properly sealed window AC unit pays for itself in energy savings within a single summer. You’ll stay cooler, your electric bill will drop, and you won't have to listen to bugs buzzing in the gap. how to seal window ac
Unroll the rope caulk and press it firmly into the cracks around the AC unit and the window frame. Use a putty knife or your fingers to smooth it out. It hardens slightly over time but remains pliable enough to peel off at the end of the season. This is the most common method and works