While it seems like you would save a bunch of money by turning your AC off while you are not home, it actually doesn’t work out that way. Air conditioners work better when they are running constantly, not being repeatedly turned on and off.
For instance, if you leave your AC off for eight hours in the summer during the hottest part of the day, when you come home it has to play catch up and crank out a lot of cool air to reach its temperature goal. The catching up the AC has to do uses a lot of energy and you will notice that you are paying for it on your next power bill.
Ideally, the best way to save money on your AC costs is to use a programmable thermostat. During the hours when you are not at home, you can program it to run a few degrees warmer. Then, you’re using less energy while away from how, but when you come back home your unit doesn’t have to work very hard to play catch up because your home is still relatively cool and comfortable.