CDL Air Brakes TestAir Brake System PartsMedium
A driver notices that the air compressor cycles on and off more frequently than usual, even when not applying the brakes. The pressure gauges show that the system pressure drops from 125 psi to 100 psi, then the compressor cuts in and builds it back to 125 psi, only to drop again shortly after. What is the most probable cause?
- AThere is a small, continuous air leak in the system.
- BThe air compressor governor is set incorrectly.
- CThe safety valve on an air tank is partially open.
- DThe air dryer is malfunctioning, causing excessive moisture.
Show answer & explanationAnswer & explanation
Correct answer: A. There is a small, continuous air leak in the system.
Frequent cycling of the air compressor without brake application, coupled with a pressure drop, is a classic symptom of a continuous air leak. The compressor works harder to maintain pressure against the constant loss of air.
Why the other options are wrong
- B. An incorrectly set governor would affect the cut-in/cut-out pressures, not necessarily cause frequent cycling due to pressure loss.
- C. A safety valve partially open would cause a continuous hiss and likely a more rapid, significant pressure drop, potentially not allowing pressure to build to 125 psi.
- D. A malfunctioning air dryer affects air quality, not direct pressure loss in this manner.
Continuous Air Leak
An unintended escape of compressed air from the brake system, leading to more frequent air compressor cycling and potential pressure loss.
- Compressor cycles more often.
- System pressure drops even without brake use.
- Needs immediate repair to prevent brake failure.
Memory trick: Leak leads to Low pressure, Compressor keeps on working.