You need to review your 2010 tax return.
There is a lifetime maximum credit of $500 for these types of energy efficient improvements. There are also sub-limits of $300 for an efficient air conditioner or heat pump, $150 for an efficient gas furnace, and $200 for efficient windows. The credit is 10% of the cost of the property only (the windows or appliances) and does not include the cost of installation.
If you installed $1500 worth of windows, the most you could have claimed is $150 credit, if all that cost was the windows and not installation. That means you have $350 left of your lifetime maximum. Depending on the cost of your new system and whether it is a heat pump or a separate furnace and air conditioner, you might be eligible for up to $350 additional credit.
You must enter the cost of the appliances not including installation, and Turbotax will ask for the amount of previous credits you claimed. If you don't have records and over-claim, the IRS will fix your return for you but it will delay payment of any refund. You should always keep tax records relating to your home for as long as you own the home plus 6 years after you sell.
You could get a transcript of your 2010 tax return to make sure what you claimed, but that will take several weeks to arrive in the mail.
