If you are 75 degrees in 100 degree weather, unless you have kids opening and closing the door all the time, you do not need a second air. I have a second air on a 40 ft, only stays at 75-79 degrees with near 100 degree ambient temp, but have 3 kids opening and closing the door all day, and my wife likes to stand in the door and talk with the door open. I think you are expecting too much out of it. Run it and forget about it, they last for years and years.