CDL Air Brakes TestAir Brake System PartsHard
A technician is diagnosing an issue where a commercial vehicle's air compressor takes an unusually long time to build up pressure from 0 psi to its cut-out pressure. All lines and fittings have been checked for leaks and found to be secure. What is the most likely cause?
- AA clogged air filter on the air storage tanks.
- BThe safety valve on the wet tank is stuck open.
- CA faulty air dryer desiccant cartridge.
- DInternal wear within the air compressor itself.
Show answer & explanationAnswer & explanation
Correct answer: D. Internal wear within the air compressor itself.
If there are no external leaks and the compressor takes an unusually long time to build pressure, it strongly suggests that the compressor itself is not efficiently pumping air. This is typically due to internal wear of components like pistons, rings, or valves, which reduces its pumping capacity.
Why the other options are wrong
- A. Air storage tanks do not typically have air filters; the compressor has an intake filter, but a clogged one would make it hard to draw air, not necessarily just slow the build-up from 0.
- B. If the safety valve on the wet tank were stuck open, it would be a massive continuous leak, preventing pressure from building at all, or building very slowly with a loud hiss, which is a different symptom than just 'unusually long time to build up'.
- C. A faulty air dryer desiccant cartridge would affect moisture removal, not the speed of pressure build-up from 0, unless it caused a significant restriction, which is less likely than internal wear.
Worn Air Compressor
Internal wear in an air compressor, such as worn piston rings or valves, reduces its efficiency and ability to pump air, leading to significantly longer times to build system pressure.
- Reduced pumping capacity.
- Increased build-up time.
- Can also manifest as excessive oil in air tanks.
Memory trick: If the tank fills slow, and no leaks show, the compressor's tired, its internal flow is low!