How do I explain how the A/C works to my foreign room mate to keep my energy costs down?

I have had 3 different room mates in my current apt, all one after the other - not living here at the same time. It's only a 2 bedroom apt. The first room mate was from Thailand, the second was American, and my current room mate is from India. For some reason, with the exception of the American room mate, I could not fully explain how the central air conditioning unit works to the point that they can understand me. The current room mate is doing the EXACT same thing that the first room mate did. Trying to talk me/force me into turning the A/C completely off during the day when we're not at home. I come home from work and its 90+ degrees in here OMG! I was taught as a child that if you turn it off like that, it takes a lot more energy to cool the place off than if you left it alone and let it maintain a certain temp, even ok to adjust like 5 degrees. Also, I was taught never to adjust the thermostat cooler than about 5 degrees at a time. Am I correct? How should I explain?

How do I explain how the A/C works to my foreign room mate to keep my energy costs down?
It's easy let him or her start paying the bill. That should fix your problem in about one month.
Reply:lock and key or duct tape over it with the words written in a 'sharpee' "HANDS OFF!!"
Reply:You are correct! Have you ever seen those plastic enclosures that have a lock and key like in government buildings? Works every time it's tried and there is no need for discussion.