Air Conditioning - Should I leave it on?

I have central air and live in Las Vegas where the mid summer temps get into three digit degrees and humidity is nil.

When leaving the house for at least 4 to 5 hours, is it best to:?

a) shut air conditioner off when I leave the house?
b) put it on a much higher setting (80 to 90 degrees)?
c) leave it run at the normal setting (around 75 to 77)

From a cost factor is it cheaper to turn it off, then turn it back on when I return, whereby it'll run constantly until it gets back to the normal setting of around 75?

BTW: The A/C is approx. 12 years old.

:eek: Check out this thread I started, maybe it'll help some

http://forum.doityourself.com/showthread.php?t=266321

Leave It on Its easyer on the unit. If you turn it off at night and open the windows you let all that humidity into the house and in the morning you fire up the unit and that pour unit has to work extra hard just to keep up so it runs longer. just set it and forget it thats all you need to do.

In humid areas I suggest setting it and forgetting it. But in your case with very little humidity, setting it up maybe 5º wont hurt. You may save a little and dropping down 5º if sized properly shouldn't take too long to cool off.