CDL Combination Vehicles TestCoupling and UncouplingMedium
When connecting the trailer's service air line (blue glad hand) to the tractor, what function does this line primarily control?
- AProvides air for the trailer's suspension system.
- BActivates the trailer's emergency braking system.
- CControls the trailer's service brakes.
- DSupplies air to the trailer's parking brakes.
Show answer & explanationAnswer & explanation
Correct answer: C. Controls the trailer's service brakes.
The blue service air line (glad hand) connects the tractor's foot brake and hand valve to the trailer's service brake system, allowing the driver to apply and release the trailer's brakes.
Why the other options are wrong
- A. Air suspension is a separate system, not typically controlled by the service brake line.
- B. The emergency braking system is activated when air pressure is lost in the red supply line.
- D. The red emergency/supply line supplies air for the parking brakes.
Service Air Line (Blue)
The air line, typically blue, that connects the tractor's service brake controls to the trailer's service brakes, allowing for active braking.
- Color-coded blue.
- Controls active braking.
- Connected to tractor's foot pedal and hand valve.
Memory trick: Blue is for Brakes.