I'm buying a new two story home 2855 sf in florida. all windows are low e and not too many windows. the house has minimal insulation per code on walls, etc.w/ concrete block first floor and wood frame second floor. this model home use to come with 2 separate ac units, one for each floor but the builder decided to install a single unit system. the builder also included a damper system to have two zones (1st and 2nd floor separated) with one thermostat on each floor. the builder first installed a Carrier 4 ton system. however, after talking to a friend i found the house should have at least a 5ton system. So i battled with the builder and he agreed to install a 5 ton system. i'm still skeptical about performance since it is hard to tell the difference between the 4 and 5 ton systems by just hanging at the house. the units he installed are Carrier ahu - fy4anb060tco and condenser 25hba360a320. is this truly a 5 ton system? what SEER #? is a 5 ton sized correctly? also when both floors are in cooling demand very minimal air comes out of some diffusers upstairs. the builder also says that it cannot cool less than 72 deg or the unit will freeze. Please advice. Your help will be greatly appreciated. Have a great day!