You need to use the a/c for at least 10 minutes every week of the year to maintain the seals because the lubricant for the system is suspended in the refrigerant. If the seals dry out, the system loses refrigerant and will need a re-gas, but if the seals are badly dried out even the fresh refrigerant will leak. I wouldn't worry about using a/c on high. If you need it, you need it. If you don't, you don't.