I think the committee should ask the strata manager to send a letter to the owner asking them to, within 30 days, either submit an application for retrospective approval via a common property by-law, with an agreement to pay for the by-law and the cost of the meeting at which the application will be considered. Failing that, within the same time frame they should remove the air conditioning unit and repair any damage done.
The CP by-law must contain agreement to maintain the common property to which the air-con unit is attached. If the retrospective by-law is refused, the owner can take action at NCAT to try to have the decision overturned. They will get the chance to present evidence of prior approval at either the EGM or NCAT hearing, if there is one.