If this was a new compressor for outside and a blower for inside (central air) then it's just as you say and is classified as residental rental real estate. That new equipment is "a physical part of" the rental property now, which is the correct line of thinking on your part. So it's depreciated over 27.5 years.
Now depending on it's cost, if when entering it as an asset if the program gives you the option to expense it, understand that it doesn't qualify for the expense option *unless* this was a case of where you only replace the broken compressor outside, or you only replaced the broken blower inside. So if it qualifies to be expensed, it's your choice. But I would recommend you expense it.
