Home › CDL Practice Tests › Combination Vehicles Questions › Question 33
During coupling, when do you supply air to the trailer and charge its system?
- A.After the air lines are connected, by pushing in the trailer air supply control and checking for leaks and brake operation
- B.Before connecting any lines
- C.Only after reaching highway speed
- D.Never, trailers use tractor air directly without charging
Correct answer
A. After the air lines are connected, by pushing in the trailer air supply control and checking for leaks and brake operation
Why
Pushing in the supply control sends air to the trailer reservoirs and releases its spring brakes when pressure builds. You then listen for leaks and confirm the trailer brakes respond.
Manual topic: Combination Vehicles - Coupling · From the Combination Vehicles practice bank (CV-033).