What action should be taken when the COMPRESSOR fault light is illuminated?

When the compressor fault light is illuminated, the appropriate action is to check the air pressure in the main reservoir. This is because the compressor is responsible for maintaining the air pressure necessary for various systems within the train, including brakes and door operations. If the fault light is on, it often indicates a problem with the air pressure supply, which could lead to failures in these critical systems.

By checking the air pressure in the main reservoir, you can identify whether the compressor is functioning properly or if there is a specific issue affecting the air pressure levels. This step is essential for diagnosing the root cause of the fault and determining the next actions needed to ensure the safe and efficient operation of the train.

Other actions, such as waiting for air pressure to normalize or activating emergency brakes, do not directly assess the source of the problem, and evaluating the door control unit would be premature without first confirming the pressure levels in the main reservoir. This systematic approach to troubleshooting helps maintain operational safety and efficiency.