Paula – most commonly, the balcony of a Lot would be part of the Lot, and even though the wall that separates a living area from a balcony would be part of that Lot in Plans registered prior to 1974, the floor upon which everything sits, including air conditioning units, is Common Property.
On the assumption that more than one Owner will at some stage seek the consent of their Owners Corporation (O/C) to install an air conditioner, I think that the tidiest way to handle all this is for your O/C to place a Motion on the Agenda for its next General Meeting whereby those in attendance may “specially resolve” to create a Register a Special By-Law (SBL) outlining the generic conditions under which it (the O/C) can consent to Owners’ air conditioning installations.
It’s advisable for a draft of the proposed SBL to also be included with the Agenda as an addendum.
In order to pass, that special resolution would need the support of ≥75% of those in attendance both personally and by proxy, with that percentage being determined on the basis of each Owner’s Lot Units of Entitlement; that is a poll vote as opposed to a simple majority vote.
If that special resolution succeeds and the resultant SBL is Registered, then yours and all subsequent requests by Owners to install air conditioners can be considered at a Meeting of the Executive Committee (E/C), and if consistent with the SBL be consented at that level.