What could indicate that air system pressure is too high?

A defective governor could indicate that air system pressure is too high because the governor is responsible for regulating air pressure in the system. When functioning correctly, the governor allows air to build up to a certain level, at which point it releases the excess pressure by venting it to the atmosphere. If the governor fails, it may either allow pressure to build up beyond the intended level or fail to release air when it reaches its set point. This can lead to dangerously high air pressure in the system, potentially causing issues like brake system failure or damage to air components.

The other options may contribute to brake system inefficiencies but do not directly cause high air pressure. A clogged air filter would restrict airflow, potentially leading to a decrease rather than an increase in pressure. Excessive wear on brake drums is indicative of braking issues and can arise from various factors, but it does not serve as a direct cause or indicator of high air system pressure. High humidity levels can affect the air supply in terms of moisture content but does not inherently indicate that the system pressure itself is too high.