A driver inspecting an older tractor finds a lever instead of a push-pull knob for the trailer air supply control. Which statement is correct?

Question

Accepted Answer

The lever has "normal" and "emergency" positions in place of push/pull, with "emergency" shutting off trailer air and setting the trailer's emergency brakes

Answer

Older vehicles use the lever only to test the air compressor governor cut-out

Answer

The lever has no equivalent function, so the tractor protection valve can't be controlled manually on older vehicles

Answer

The lever only works below 20 psi and has no effect above that pressure