______Check the working condition of the AIR CONDITIONER.

Honestly I do not know why the previous owner spent so much on the furnace and Air conditioner when the house needed so many other things like windows!  

Then, if there's a need, and your market checks out then start getting it furnished and add all of the amenities, towels, body wash/soap/shampoo/conditioner, washer/dryer, etc. 

Looking for company in Norman Ok to sale and install air conditioner in rent house.

Should I buy a central air conditioner?

I would expect similar results with an air conditioner in an attic space that is over 100F.In such cases, looking at the building as a whole - rather than independently at individual systems and sub-constructs -  it may make more overall energy sense to turn the attic into a conditioned space.Now, how do you address the issue of thermal bridging?

These days, when I install hot water tanks, room air conditioners, my CPA would expense them.

That's because the combustion byproducts are in a liquid form, so they need to be drained out of your home in a similar way the condensation from an air conditioner is drained outside.At least, that's my understanding of it.

Some years the yields really are that good, some years they are closer to zero (like when a roof and air conditioners need to be replaced - these things happen).Also, you mentioned increasing rent - having a steady tenant who actually pays their rent is much more valuable than pushing someone out and dealing with a couple months of vacancy for an extra $50/months in my experience.

I also had an air conditioner fail on move-in day in 100 degree heat.