What is purpose of pull lever on top right of decorative panel

It's an air intake vent damper. If you push it in, the unit won't pull any air from outside, instead it'll recirculate air from the room. If you pull it outward, it allows the unit to pull air from outside. During the day when it's hot outside, the lever should be pushed into the closed position to allow for more efficient cooling. At night, if you want to exchange air from outside when it's cool enough, pull out the lever to allow that to happen. The unit will exhaust hot air no matter if this switch is in or out.

I cannot tell you according to model number. I'm sure it is the exhaust lever. Almost all window or through wall air conditioners have a lever that opens a little door in the back of the air outlet duct. When open it exhausts some of your room air outside. Basically you are using your air conditioner as an exhaust fan when this is open and blowing most of the air that your unit has cooled outside. Allot of times the wire going from the lever to the door or the plastic is broken not letting this door open or close. If you take the front cover off of the air conditioner and look in the duct where the cold air comes out of the front of the unit you can actually see this door or the opening that it closes. Make sure it is shut and your air conditioner will cool much more effectively. This is probably when the lever is pushed in.