CDL Air Brakes TestAir Brake System PartsEasy
A driver is inspecting the air brake system on a commercial vehicle. They notice that the air compressor builds pressure from 85 psi to 125 psi in less than 45 seconds while the engine is idling. What does this indicate?
- AThe air compressor is functioning correctly.
- BThere is a significant leak in the air brake system.
- CThe air storage tanks are overfilled.
- DThe air compressor governor is set too high.
Show answer & explanationAnswer & explanation
Correct answer: A. The air compressor is functioning correctly.
CDL regulations require that the air compressor build pressure from 85 psi to 125 psi within 45 seconds for a properly functioning system. Meeting this standard indicates the compressor is working as expected.
Why the other options are wrong
- B. A significant leak would cause the compressor to take longer to build pressure, or it might not reach the required pressure at all.
- C. Air storage tanks cannot be 'overfilled' in a functional system; the governor prevents excessive pressure.
- D. A governor set too high would allow pressure to build above 125 psi before cutting out, which is not indicated here.
Air Compressor Build-Up Rate
The speed at which the air compressor can increase air pressure in the system, a key indicator of its health.
- Must build from 85 psi to 125 psi in 45 seconds or less.
- Test performed with engine at idle.
- Indicates compressor efficiency and system integrity.
Memory trick: A quick puff means the compressor's tough!