Crappy Lanlord in KY what to do?

[Sarah Spinosa]

I have a friend who’s landlord keeps neglecting to replace their broken HVAC system. She has not had heating or air since August (practically since the time she has moved in). She calls weekly asking for him to repair it/update and he gives her the run around. What can she legally do? Not pay rent? Is the landlord required to fix this? Any help would be great! Thanks!