I have a 4 ton trane XLI1400 and it has been adequate the past several years here in central Florida. Since, I have added 300 square feet of A/C space. What I really need is a 4.5 ton, but since they don't make it and putting in a 5 ton requires complete rework of the ducting, we have decided to stick with the 4 ton until it breaks - it is 7 years old. Certain times when it is very hot outside, the A/C can only get the temp down to 79 and no more. Coming out of the registers is 65, which is pretty good considering the outside temp is 93 or so.
My question: I can change the CFM of the fan from 400 to either 350 or 450 by changing some dip switches. Would either improve my cooling? Or does it really matter?