How do you diagnostic AC system on Peterbilt trucks?

To diagnose the AC system on Peterbilt trucks, start by checking the refrigerant levels and inspecting for any visible leaks in the components, such as hoses and connections. Next, test the electrical system, including the compressor clutch, fuses, and relay, ensuring they function properly. Additionally, examine the AC control panel for any faults and use a pressure gauge to measure the high and low-side pressures. Finally, check the cabin air filter to ensure proper airflow and assess the temperature output from the vents.