First start truck and build AIR PRESSURE to approximately 120 PSI. Place truck in 1st gear, turn engine (Key) off and then turn key ON but do not start the engine.
Release brake valves (red & yellow) and let AIR PRESSURE STABILIZE. NEXT, check for one minute, vehicle should not lose more than 3 PSI.
Put 90 pounds of AIR PRESSURE (Hard Brake) on foot valve and hold for one minute, vehicle should not lose more than 4 PSI.
Pump foot valve until AIR PRESSURE drop to approx. 60 PSI, warning light or buzzer should come on then.
Continue to pump foot valve until AIR PRESSURE drops between 40 and 20 PSI. Red and yellow (Trailer Air Supply – Parking Brake) buttons should then pop out.
Place transmission in neutral, start truck and build AIR PRESSURE
back up to approx. 120 PSI. This completes the AIR BRAKES
TEST.
3, 90, 4, 60, 40, 20 . . . . = PSI Marks.
TERMINOLOGY
AIR PRESSURE = The PSI is indicated by the gauge or gauges on the dashboard. Primary and Secondary, there may be one or two gauges.
APPLICATION GUAGE = It goes up when foot valve is pushed down to 90 pounds.
STABILIZE = The position the Air gauges fall to once the Valves are released and PSI stops falling.
VALVE = The Red (trailer air supply) and the Yellow (Parking brake) control BUTTONS, PUSH to RELEASE and PULL to APPLY.
FOOT VALVE = Brake Pedal. Some trucks also have a Hand Control, trolley valve.