Replaced Rental Furnace and Air Conditioner

I spent $6,500 on a new furnace and air conditioner for my rental.  It looks like a need to set it up like a new asset like property and depreciate it over 27.5 years.  I see that if it was less than $2,500, I could use the Safe Harbor.  Can I just take the safe harbor for $2,499 this year instead?  Can I use the safe harbor for Small Projects or Routine Maintenance?  Can I use Section 179?  Any help clarifying this would be greatly appreciated.