For best results, Always keep your thermostat at 78 degrees… turning it down to 70 WON’T cool your home any faster.  If your AC system does not seem to be working right, make sure that the thermostat is set lower than the actual room temperature.  Also, the selector switch should be on "cool".  If the thermostat is programmable, be certain it has fresh batteries.  Check for power by moving the fan switch from "auto" to "on". If the blower runs, there is power. If nothing happens, a control is burned out or power is disconnected. If the system uses a furnace for heat, check that the emergency switch is on. If you are familiar with the fuse or circuit breaker panel, check for blown fuses or tripped breakers.