Air Cooled Split Unit (ACSU) lifespan can last 10~15 years. Post this duration, if the unit no longer deliver the coolness after the regular preventive maintenance, then you can consider to get a new one.

2ndly, usually the manufacturer will keep the spare parts for 7 years only. If repairing is getting harder / cannot find the spare parts of the faulty component, then it is recommended to get the new one.

3rdly, if your unit is using R22 refrigerant, just change and get the new one. R22 refrigerant has been phased out due to ozone depletion characteristic.