Bummed, barely used AC already Not Performing.

Return air goes thru filter then thru evap coil to get chilled then over to discharge plenum where it get blown into rig
The wall between return side and discharge side should be sealed so cold/warm air no not mix.

That is the 'divider'

Also........2013 year.
Have you ever cleaned the return air filter?

They are NOT your household type filters that can go a whole season .....once a month even when not being used much. Just a thin foam filter.
Also evap coil.it gets dirty....poor cooling capability