A- Remember that heat rises and there is a large heat load on the roof of your home. Unless you have a separate system for the second floor, the thermostat will be located on the 1st floor. When the temperature on the 1st floor satisfies, the thermostat turns the A/C system off. If the thermostat is on the first floor it can’t recognize the warmer 2nd floor. Proper attic insulation, correctly sized ductwork and Zoning may help the temperature difference.