Not sure in Victoria. In the ACT (and you might have something similar to look for) the EC can approve ‘minor uses’ of common property if they are ‘unlikely to unreasonably interfere with the reasonable use and enjoyment of the common property’. Examples in the Act include air conditioners and awnings. If the air conditioner is in an unobtrusive location, neither unsightly nor blocking any access, then the EC (in the ACT, perhaps in Vic also) could resolve to give approval. Non-minor uses of common property requires a ‘special privilege’ to be granted to the unit owner at a general meeting. Again, you might have something similar.