No. The total cost of a new air conditioner is reported on the tax return for the year it is installed and ready to be used (known as the "in service" date). The Safe Harbor Election is available only in the first year the asset is used. You can claim the entire cost (including installation costs), even if you are paying over time.
Additional Information:
This AC unit was purchased because the original unit failed and renters were suffering. I was restoring property to original condition, not trying to make upgrade or improvement. I consider this to be a repair and want to expense it that way. Additionally, I am retired and have had no tax liability for 2 years now. Nothing changes on my return but now I have to pay someone to do my taxes b/c I do not know how to do this.
A replacement is NOT a repair, it is a replacement. If you purchased a new unit, then it is an asset. You would write it off or list it as an asset in the year you put it in service. Since you did this 3 years ago, you would need to amend your return for that year.
If you do not want to amend the return, you can just leave it go. It would result in a refund, so there is no tax penalty for not taking your refund.