CDL Air Brakes TestAir Brake System PartsMedium
A driver notices that the air compressor is continuously running, but the air pressure gauges are not increasing beyond 80 psi. Which component is most likely malfunctioning?
- AThe air storage tanks are overfilled.
- BThe low air pressure warning system has failed.
- CThe safety valve is stuck open.
- DThe air compressor governor is stuck in the 'cut-in' position.
Show answer & explanationAnswer & explanation
Correct answer: D. The air compressor governor is stuck in the 'cut-in' position.
If the air compressor is continuously running but pressure isn't building, it indicates the governor isn't telling it to stop, and pressure isn't reaching the 'cut-out' point, suggesting it's stuck in the 'cut-in' position or there's a significant leak.
Why the other options are wrong
- A. Overfilled air tanks would cause the safety valve to open, not prevent pressure buildup while the compressor runs.
- B. A failed low air pressure warning system would not affect the compressor's operation or pressure buildup.
- C. A stuck-open safety valve would cause air to vent, preventing pressure buildup, but the governor might still attempt to cut out.
Air Compressor Governor
The air compressor governor controls when the air compressor pumps air into the air storage tanks. It has 'cut-in' and 'cut-out' pressures.
- Set to cut-out around 125 psi and cut-in around 100 psi.
- Stops the compressor when tanks are full ('cut-out').
- Starts the compressor when tank pressure drops ('cut-in').
Memory trick: Governor's got the compressor's 'go' and 'stop' signals.