... However, the leasing office is stating that had we changed the filters more often we wouldn't have needed to have a tech come out. AND, she mentioned that in the lease it states that the tenant is responsible for any damage and/or repairs they cause to any walls, appliances, etc. The AC unit falls under the etc clause.
Question - are you expected to change the filter in the AC? I would not think so as it is the leasing company's property. Same as you should not need to do any sort of maintenance to say to any other appliance that comes within your unit.
Yes basic cleaning - but not replacing things. You should not be responsible for normal wear and tear for example like replacing a filter or replacing old pipes in your sink, however, you would be responsible for say throwing the AC unit in a fit of rage or breaking the sink handle when you dropped a sledge hammer on it.
Did the "tech" replace the filter that needed replacing? Then he isn't doing his job.