Saying "when a new a/c breaks down after only 7 months of use, because it was only turned off twice in an entire summer, then I WILL raise an eyebrow because the money for that air conditioner or appliance comes out of MY pocket. So it's not rocket science that any LL would prefer a tenant not be home as much so that such "wear and tear" incidents are minimized.." was a typo?
That's one heck of a typo.
Personally, I never turn my a/c off in hot weather. It takes too long to cool the place down afterward. I raise the temp when I'm leaving the house, but I don't turn it off. Unless your a/c came with warning that it must be turned off three or more times each summer and you included that in the lease, you have no call to get pissy with the tenant if it breaks.
You just don't want the tenant here because he/she nailed you on your greed and lack of logic. Perhaps you should start advertising "condo for rent for 18 hours a week." Assuming you're willing to reduce the rent accordingly, of course.