1. Keeping the a/c cooling the house all day uses less electricity than turning it off and then back on in the evening or when you return from a vacation.
2. Running the a/c a few degrees colder at night cools the big cement slab that the house is built on, and thus saves electricity during the day (the a/c is set back to normal living temperature during the day).
2b. If the temperature inside the house reaches 78 F at 10 AM on both days with the a/c set colder the previous night, and also when it was just set normally the previous night, then that proves setting it colder made no difference.
3. The a/c uses less current at night ( you measure it with an ammeter as it is running ).
4. The a/c uses less current if you spray the outside unit with the garden hose and then measure it with the ammeter.
5. Shading the outside unit (compressor and condenser) does not reduce electricity costs [Assume shade does not block air flow].
6. If you have high ceilings and ceiling fans, it is more energy efficient to leave the fans running at low speed all the time to pull down hot air and get it to circulate through the a/c system.
7. It isn't worthwhile to check on the amount of Freon (or whatever) that is in the system -- all that matters is measuring the temperature of the cold air coming out (say 62 F) and the outside temperature or maybe the attic temperature.