Is it better to leave AC on constantly?

Is it better to leave AC on constantly depends on what you mean by constantly, and answer is it is better to leave AC on at constant temperature with auto fan, but raise temperature 7 to 10 degrees when away, rather than turning off completely or leaving at same low temperature all day when away. Leaving AC at same 72 degrees 24/7 when you are away at work wastes energy cooling empty home, costing extra 10 to 15 dollars per day in hot climate. Turning AC completely off causes home to heat up to 85 to 90 degrees, with walls and furniture storing heat, so when you return, AC must run continuously for 3 to 5 hours to remove stored heat, using more energy than if you had left it at higher setpoint, plus humidity rises to 70 percent encouraging mold. Best practice for savings is programmable thermostat to set AC 7 to 10 degrees higher when away, for example 78 to 80 degrees when away and 74 to 75 degrees when home, saving 10 percent per DOE. For variable speed AC like Trane XV20i, leaving on at constant temperature is more efficient than on-off cycling because variable runs at low speed most efficiently at 30 to 40 percent capacity. Constantly running fan on uses extra electricity at 20 to 40 dollars per month. So leave AC on constantly at setpoint when home, use setback when away, do not turn off completely.