@Doninflorida
You are correct that installing equipment in two different years would be eligible for 2 different credits, this has always been the case. What is new with the Inflation Reduction Act is the removal of the lifetime cap. The A/C credit used to have a cap of $200 per year and $500 lifetime. Now it is $600 per year with no lifetime cap, so the idea of splitting the job between years becomes a more useful strategy.
However, the property must be claimed when installed, not when it is convenient to do so. If the property was installed in 2023, you must claim both items on your 2023 return. If you lie and claim one in 2024 and get audited, you will lose because that is clearly against both the instructions and the law.
In the case of a very large home with two A/C systems, the language "each item" in the law would seem to indicate that you are eligible for $1200. However, the form is designed to only allow $600. What you need is a way to claim $1200 in 2023, then you get audited, and if the IRS rules against you, you go to Tax Court and argue that the forms and instructions are incorrect because they disagree with the law (the law controls--if the regulations or instructions are in conflict with the law, the law is supposed to control).
You might (this is not advice) list one AC on the AC line and list the other on the "boiler/furnace" line. That would get you $1200. Then, if audited, you would need to make your case that even though you listed the property on the wrong line against the instructions, the result was correct according to the law. This strategy poses a certain amount of risk, and I would suggest checking with your own hired tax professional.
