The cost of fixing an AC unit can be attributed to several factors. Firstly, the complexity of the repair plays a major role; more intricate issues require specialized skills and more time to resolve. Secondly, the parts needed for the repair can be expensive, especially for high-efficiency or newer models. Lastly, the expertise of certified HVAC technicians is a crucial factor, as their training and experience ensure that your AC unit is fixed correctly, which commands a premium.