How can you test that air flows to all trailers?

The correct method to test that air flows to all trailers involves letting the air build up, pushing in the red trailer supply knob, and then checking the last trailer. This process ensures that the air pressure is sufficient to deliver air to the entire braking system for all trailers connected to the tractor.

When you allow the air to build up and engage the supply knob, you are actively confirming that air is indeed moving through the system. This is critical because each trailer’s brakes depend on the air supplied from the tractor. By checking the last trailer after engaging the supply knob, you can observe whether the air is reaching that trailer's braking system effectively. If the brakes are not functioning properly, it indicates a problem in the air distribution.

Other methods like checking the pressure gauge can provide useful information about the overall air pressure but do not directly test if air is flowing to each trailer. Listening for air escaping is also insufficient, as it does not confirm the presence of air at each trailer’s brake system. Using a pressure sensor tool could be useful in diagnosing pressure levels, but it is not a practical or direct method for establishing airflow to all trailers during a routine check. Thus, the recommended approach is the one that involves actively testing the air supply through the trailer supply