CDL Air Brakes TestAir Brake System PartsHard
A technician is performing a diagnostic check on an air brake system. They notice that the air compressor is constantly running, but the system's air pressure never exceeds 80 psi. All connections appear secure, and there are no audible leaks. What is the most probable cause?
- AA completely blocked air dryer.
- BA worn-out or damaged air compressor.
- CA faulty air compressor governor set too low.
- DA severe restriction in the air intake line.
Show answer & explanationAnswer & explanation
Correct answer: B. A worn-out or damaged air compressor.
If the compressor is constantly running but cannot build pressure above a certain point (e.g., 80 psi, far below normal operating range of 100-125 psi), even without leaks, it strongly suggests the compressor itself is worn out or damaged and can no longer generate sufficient pressure.
Why the other options are wrong
- A. A completely blocked air dryer would prevent air from reaching the tanks, but the compressor would likely build pressure to its cut-out point before the dryer or stall.
- C. A governor set too low would cut out at 80 psi, but the compressor would stop running, not run constantly.
- D. A severe intake restriction would prevent the compressor from drawing enough air, leading to low output, but 'constantly running' points more directly to the compressor's pumping ability.
Worn Air Compressor
An air compressor with internal wear or damage that prevents it from generating or maintaining sufficient air pressure, even when running continuously.
- Runs constantly without reaching full pressure.
- Internal components (e.g., piston rings) are worn.
- Requires replacement or overhaul.
Memory trick: Compressor Cries, but Can't Create enough pressure.