Fair wear and tear refers to the gradual deterioration that occurs through normal, everyday use of a property and its fittings. For air conditioning units, this typically includes minor dust accumulation, slight fading or discolouration of panels, and general aging of components over time. Damage caused by the tenant, such as a broken panel, failure to clean filters leading to a blocked unit, or using the AC outside its intended purpose, would not be considered fair wear and tear and could be charged to the tenant at the end of the tenancy.