I am not an air conditioner technician, however, I had a big problem with my new AC unit in my newly built 2450 square foot home in hotter-than-hell Texas not being able to keep my home at the 72F set on the thermostat. I had about 4 technicians tell me that the unit was working fine, but when the temperature kept creeping up approaching 80F, I called the manager of the AC company. He came out and just looked at everything, no tools involved. He told me that an AC unit, like a performance car engine, works better if you can improve the way it breathes. He advised me to add an additional air return duct and filter. I did this myself and all my problems were cured. A cheap and easy fix!