No, the LLC does not change the character of the property. It is still residential, which does not qualify for Section 179.
However, it MIGHT qualify as a repair/maintenance. The fact that it is only one out of four (a small portion of the total) would likely qualify it. However, the fact that the building is four separate units and each HVAC performs only within that unit (making it a large portion of the total in each unit) makes me hesitate to assert if it would qualify.
If you want to read the legalese, below is the link to the Regulation that I am referring to. It has SEVERAL examples (at least three pertinent ones) involving HVACs, so be sure to read them all before making your decision (you can hit Control-F on your keyboard and type "HVAC" to search for the 70 occurrences of that word).
https://www.law.cornell.edu/cfr/text/26/1.263(a)-3
