You can research the cost of the AC unit and the Furnace and Blower on the internet to have an approximate idea of the cost for each energy-efficient item that was included on your receipt. If the AC unit is $2500 and the Furnace and Blower are $5000, the receipt for $7500 would be divided by 1/3 and 2/3rds. Since you have the receipt your expenses are backed up if there are any questions from the IRS.
The air-conditioning and the furnace are entered on separate lines. The air conditioner is eligible for up to $300, and the furnace is only eligible for up to $150. The credit is 10% of the amount of the appliance. If you are audited, you will need to show something that supports how you allocated the cost between the furnace and the air conditioner.