Final answer:
The first step in the air-conditioning diagnostic process is carrying out a performance test to check temperature, pressure, and component function.
Step-by-step explanation:
Carrying out a performance test of the air-conditioning system is the first step in the diagnostic process. This type of test usually involves checking the temperature of the air being blown into the vehicle, measuring the pressure levels within the system, and ensuring that all components, such as the compressor, condenser, and evaporator, are functioning correctly. A performance test will typically indicate if there's a significant issue that requires further investigation, such as a leak test or a diagnostic test with specialized equipment.