Where do I put in cost of new air conditioner on my rental home? in maintenance or depreciation? Thanks

Window unit?  Central air conditioning installed?

This is an asset that has to be depreciated. If it is a wall unit than can be removed, you will depreciate it over 5 years. If it is a central unit, depreciate it over 27.5 years, just like the building itself.

https://www.irs.gov/pub/irs-pdf/p946.pdf