No, you can't claim a 2015 tax item on your 2016 income tax return. If the A/C unit qualifies, you would have to amend your 2015 income tax return. See How do I Amend (Change or Correct) a 2015 Return in TurboTax?
To see is your A/C unit qualifies, click on Energy-efficient heating, ventilating, or cooling systems
Please note, not all ENERGY STAR qualified products qualify for a tax credit. ENERGY STAR distinguishes energy efficient products which, although they may cost more to purchase than standard models, will pay you back in lower energy bills within a reasonable amount of time, without a tax credit.
To enter, click on Where do I enter qualified energy-saving improvements?
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