The recent tax act changed special depreciation to 100%. If you want to only take 50% for depreciation this year, you can select I'll take partial section 179 deduction this year (on the same screen where you selected special depreciation).
As long as the HVAC was purchased and placed in services for your business or rental, you'll have this option. Also, there are thresholds for purchasing new assets, but you'll see the total amounts you have available when you select the option.
Let me know if you have any questions.
