CDL Air Brakes TestAir Brake System PartsMedium
A driver notices that the air compressor cycles on and off more frequently than usual, even when the vehicle is not being driven or using air accessories. What is the most likely cause?
- AThe air compressor governor is set too high.
- BThe air dryer is saturated and needs replacement.
- CThere is an air leak somewhere in the system.
- DThe brake pedal (foot) valve is stuck open.
Show answer & explanationAnswer & explanation
Correct answer: C. There is an air leak somewhere in the system.
If the air compressor is cycling more frequently without active air use, it indicates that the system is losing air pressure faster than it should. This is a classic symptom of an air leak somewhere in the air brake system, forcing the compressor to work harder to maintain pressure.
Why the other options are wrong
- A. A governor set too high would cause the compressor to build to a higher pressure before cutting out, but not necessarily cycle more frequently without air use.
- B. A saturated air dryer reduces its ability to remove moisture, potentially leading to system contamination, but wouldn't directly cause frequent compressor cycling due to pressure loss.
- D. A stuck-open brake pedal valve causes a continuous leak from the brake chambers when the brakes are not applied, which is a specific type of air leak, but 'an air leak somewhere in the system' is a broader and more accurate encompassing answer.
Continuous Air Leak (Compressor Cycling)
An unintended escape of compressed air from the air brake system, often indicated by the air compressor cycling on and off more frequently than normal to compensate for the pressure loss.
- Leads to increased compressor workload.
- Causes faster-than-normal pressure drop.
- Requires immediate inspection and repair.
Memory trick: Cycling Compressor Cries 'Leak!'