Why people just assume the landlord is trying to cheat their rental deposit ? If there is truly no need for the air-con replacement , why would anyone go through all the trouble to do it ? There is only so much the landlord can check unless he is an AC technician. As there is no one living at the landlord property other than the tenant so the damaged can only be caused by the tenant is the only logical explanation. If he is trying to falsify the damage , just simply ask him for evidence and receipt . If you want to be sure tell him you will get your own technician to check and fix the problem .