You won't deal with this at all, in any way, form or fashion on your 2017 return. You'll deal with it on the 2018 return, since you will not be converting it from personal use to rental until 2018. So just keep all your paperwork and wait until then.
On the 2018 return you'll enter the new A/C unit (central air I presume, and not a window A/C unit) as an asset in the assets/depreciation section of the program. But like I said, you'll deal with those details next year, when you file the 2018 return.
Meanwhile in the answer box below, I've posted information that you'll need next year. So I suggest you print it out and keep it with your 2018 tax information. I can't stress the importance of getting things PERFECT on the tax return in the first year you report rental income. Just one teeny-tiny mistake can grow exponentially over time. Then when you catch the error years down the road (assuming the IRS doesn't catch it first) correcting it can be quite $costly$ tax-wise. So in the first year of reporting rental income, absolute perfection is not an option... it's an absolute must.
