CDL Air Brakes TestAir Brake System PartsHard
A technician is performing a diagnostic check on a commercial vehicle's air brake system. They observe that the air compressor takes an unusually long time to build from 85 psi to 125 psi. Which of the following is the most likely cause?
- AA malfunctioning spring brake control valve.
- BA faulty low air pressure warning switch.
- CAn improperly adjusted slack adjuster.
- DA restricted air intake filter on the compressor.
Show answer & explanationAnswer & explanation
Correct answer: D. A restricted air intake filter on the compressor.
A restricted air intake filter starves the air compressor of air, significantly reducing its efficiency and increasing the time it takes to build pressure.
Why the other options are wrong
- A. A malfunctioning spring brake control valve would affect parking brake operation or air leaks, not the compressor's build-up rate from 85 to 125 psi directly.
- B. A faulty warning switch would affect the indication of low pressure, not the rate of pressure build-up.
- C. Slack adjusters affect brake application and release, not the air compressor's ability to build pressure.
Air Compressor Intake Restriction
A blockage or restriction in the air compressor's intake system (e.g., a dirty air filter) that reduces the amount of air available for compression, leading to slow pressure build-up.
- Causes the compressor to work harder.
- Increases the time required to reach cut-out pressure.
- Can lead to compressor overheating and premature wear.
- Often indicated by a drop in air delivery volume.
Memory trick: When the compressor's breathing is hard, pressure builds slow and scarred.