CDL Combination Vehicles TestCoupling and UncouplingMedium
When connecting the trailer's emergency air line (red glad hand) to the tractor, what is its primary function?
- ATo control the trailer's parking brakes independently.
- BTo activate the trailer's anti-lock braking system (ABS).
- CTo provide continuous air pressure for the service brakes during normal operation.
- DTo supply air to release the trailer's emergency brakes and charge the air tank.
Show answer & explanationAnswer & explanation
Correct answer: D. To supply air to release the trailer's emergency brakes and charge the air tank.
The emergency air line (red glad hand) supplies air from the tractor to the trailer's air tanks, which then charges the system and releases the spring-actuated emergency brakes.
Why the other options are wrong
- A. While it affects parking brakes, its primary function is to supply air and release the emergency brakes, not independent control.
- B. ABS is controlled by the electrical cable, not the air lines directly.
- C. This describes the function of the service air line (blue glad hand).
Emergency Air Line (Red)
The air line (connected via a red glad hand) that supplies air pressure from the tractor to the trailer's air tanks, releasing the trailer's spring-actuated emergency brakes.
- Red glad hand connection.
- Charges trailer air tanks.
- Releases trailer emergency brakes.
- If disconnected, trailer emergency brakes apply.
Memory trick: Red is for Release, Blue is for Brake!