You can't take this deduction for residential rental property. There may have been some confusion because if you also offer services such as meals or cleaning, then it is reported on Schedule C and it is a business.
The law known as the Tax Cuts and Jobs Act (TCJA), P.L. 115-97, makes HVAC costs eligible for expensing under Sec. 179. To be eligible, the HVAC costs must be for nonresidential real property that is placed in service after the date the property was first placed in service.
Also, you mentioned claiming it as an expense. This is the de minimus safe harbor election, not section 179. Your HVAC cost more than the allowed $2,500.
