What is indicated by excessive air reservoir build up time?

Excessive air reservoir build-up time typically indicates that there is a restriction preventing adequate airflow into the air system. This aligns with the idea of a restricted compressor air inlet, as such a restriction would impede the efficient operation of the compressor, causing it to take longer to build up the necessary air pressure in the reservoirs.

When the air inlet to the compressor is restricted, the volume of air that the compressor can draw in is reduced, which directly impacts its ability to generate the required pressure quickly. This results in a longer than normal build-up time for the air reservoirs. Identifying and rectifying a restricted air inlet is crucial for restoring the proper functioning of the air brake system, ensuring that systems relying on compressed air operate efficiently and safely.

The other answer choices point to different issues within the air system that would not specifically result in excessive build-up time: a plugged air dryer might affect air quality but not build-up speed directly; an air governor set too low would lead to premature cut-out, not longer build times; and a leaking service relay valve could cause loss of pressure but would not create a prolonged build-up scenario.