CDL Air Brakes TestInspecting Air Brake SystemsHard
A technician is performing a diagnostic check on an air brake system. They notice that the air compressor struggles to build pressure, and when it finally reaches cut-out pressure, it takes an excessively long time (more than 3 minutes to go from 85 to 100 psi). What is the most likely cause?
- AThe air dryer is malfunctioning and continuously purging.
- BThe air compressor itself is worn or faulty.
- CA leak in the air system, causing constant air loss.
- DThe low air warning device is stuck in the 'on' position.
Show answer & explanationAnswer & explanation
Correct answer: B. The air compressor itself is worn or faulty.
If the air compressor takes an excessively long time to build pressure, especially beyond the specified limits (e.g., more than 3 minutes from 85 to 100 psi in a dual air system), it indicates a worn or faulty compressor that cannot produce air efficiently. While leaks can contribute, an 'excessively long time' points to the compressor itself.
Why the other options are wrong
- A. A continuously purging air dryer would definitely extend build-up time by causing a constant leak, making this a plausible distractor.
- C. A general leak in the air system would also extend build-up time, similar to option A, but 'struggles to build' suggests the compressor's output itself is weak.
- D. A faulty low air warning device would not affect the rate at which the compressor builds pressure.
Slow Air Pressure Build-Up
Slow air pressure build-up, taking longer than specified times (e.g., 3 minutes from 85 to 100 psi), often indicates a worn air compressor or a significant air leak.
- Compressor efficiency is compromised.
- Can be caused by internal wear or a large leak.
- Requires diagnosis of compressor or leak source.
Memory trick: Pressure's slow to rise? Compressor's seen better skies!