I think most state and territories have a principle that ‘utility conduits’ that service a single unit are the responsibility of that unit, even where they traverse common property. So, I would be inclined to apply that principle to the air conditioners. You could probably make an argument that the pipes and system that circulates refrigerant fluid into each unit is providing a utility service (heating or cooling).
Where I am, we added a general rule (ACT-speak for bylaw) to make explicit and beyond doubt that anything that services an individual unit is that unit’s responsibility to repair and maintain, even if it is on common property, with or without permission to be there.