Air Break Practice Test

Results

#1. How can you tell if you have cross-connected the supply line and the service (control) line on a tractor-trailer with air brakes?

(a) The trailer parking brakes will not release.

(b) The trailer service brakes will not function.

Both (a) and (b) will happen.

If you cross-connect the air lines, supply air will be sent to the service (control) line instead of the trailer air reservoirs. Reservoir air will not be available to release the trailer spring brakes (parking brakes). And when you press the brake pedal, service air won’t flow to the trailer brake chambers or relay valves, so the service brakes won’t work either.