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While coupling, a driver accidentally crosses the air lines, connecting the service line to the supply gladhand and the supply line to the service gladhand. What will happen when the system is charged?
- A.The trailer brakes will not work properly: the supply air goes where the service signal belongs, so the driver cannot control the trailer brakes the normal way
- B.Nothing changes, because the two lines carry identical pressure at all times
- C.The trailer tires will inflate to maximum pressure through the service line
- D.The fifth wheel will unlock automatically as a safety response
Correct answer
A. The trailer brakes will not work properly: the supply air goes where the service signal belongs, so the driver cannot control the trailer brakes the normal way
Why
Crossed lines put supply pressure into the service circuit and leave the driver without normal control of the trailer brakes. This is why the lines and gladhands are color-coded and why you test trailer braking right after coupling.
Manual topic: Combination Vehicles - Air Lines and Gladhands · From the Combination Vehicles practice bank (CV-242).