This must be one of the most common requests by lot owners and so the first thing to do is see if a SBL is already registered for your strata and if so use that as the template and just put in your details. Also check if any other owners have a/c installed without a SBL.
Their are more than 2,000 members on this site surely one of them could provide a copy of a suitable generic bylaw (I cannot because we don’t have this issue in QLD) that you could use. Bear in mind if this vote doesn’t happen at the AGM then you could be up for the costs of an EGM as well.
Doing the right thing in NSW Strata is a bottomless pit of costs to the person who want to do it right.
One thing doing it Whales way you not only need the motion to install the a/c approved by 75% but you then need the SBL to be approved by the same 75% as well. So skip the motion just submit a SBL for the a/c unit which saves having 2 votes.