I thought it was what people on a diet can order at Dairy Queen.

You might check this out:

In December 2019, the U.S. government renewed the 25C tax credit for high-efficiency heating and cooling equipment.

What it covers

• ...
• $300 maximum credit available for qualifying central Air Conditioners, Heat Pumps, Packaged Units and Ductless Mini-Split Systems

https://www.lennox.com/owners/tax-credits/energy-tax-credits