Truck and Trailer Combination Air Tests (with extra details)
- Ensure wheels are chocked, check compressor and governor if not done on pre-trip inspection.
- Dump air tanks, starting with wet tank. This order allows you to make sure the one-way check valves between the wet tank and primary and secondary air tanks are functioning.
- Start engine, low air pressure warnings (visual and audible) should be activated and shut off no lower than 60 psi.
- Measure the time required for pressure buildup between 85 psi and 100 psi, which cannot be more than 2 minutes at a max of 800 engine rpm.
- Governor should cut out compressor between 120 psi and 145 psi.
- Supply air to trailer (push red valve), then release tractor park brakes (push yellow valve). Governor will typically cut in the compressor 20 to 25 psi below cut out, but cut in must happen no lower than 100 psi.
- Build to max air pressure, then shut down engine and test the tractor protection system:
- "break" the service (blue) glad hand, there should be no air loss from tractor or trailer
- "break" the supply (red) glad hand, there should be
- no air loss from trailer (other than the line dumping which should be hardly noticeable)
- trailer brakes dynamite (spring brakes immediately apply)
- air loss from tractor should stop with no less than 20 psi remaining in tanks
- check that trailer brake slack adjusters are at approximately 90 degrees to the pushrods, which means the brakes are applied
- after the supply line has stopped dumping air, step into the cab and
- make sure that the trailer supply valve (red) has popped out, but not the tractor park brake valve (yellow)
- turn key on (don't start) and check air pressure gauges, air pressure should be no lower than 20 psi
- make a full foot brake application and hold it for a few seconds as you listen for air loss through service line, check air pressure gauges for signs of air loss, should be none
- reconnect glad hands
- Start engine, supply trailer with air (push red valve).
- Build to max air pressure, then shut off the engine and turn the key back on (don't start the engine).
- Make a full foot brake application and hold it for 1 minute, during which there can be no more than 4 psi air loss after the drop from the initial application.
- Fan the brakes to lower air pressure, the low air pressure warning should come on no lower than 60 psi.
- Continue to fan the brakes, and watch for
- the trailer air supply valve (red valve) should pop out no lower than 20 psi
- the tractor park brake valve (yellow valve) may not pop out, but the tractor park brakes must apply no lower than 20 psi
- Start engine, immediately put into first gear and "tug" (gently attempt to drive away). The tractor park brakes should be applied, in which case the cab would rock up on the driver side, and the tractor not move.
- Shift back to neutral, put away chock blocks.
- Supply trailer with air after low pressure alarms go off, and wait for "working pressure", minimum 100 psi.
- Shift into first gear, leave there for remaining tests:
- do another tug on the tractor park brakes, they should still be applied and the cab should rock again
- dump the trailer air (pull the red valve), release the tractor park brakes (push the yellow valve), and tug on the trailer spring brakes, they should be applied and the tractor should pull straight ahead slightly, then lightly "bounce" back
- supply the trailer with air and roll ahead, then pull the trailer brake hand valve, and the truck should stop without any nosedive, and lightly "bounce" back
- roll ahead again, and then make a brake application with the pedal, the nose of the truck should drop as the truck stops sharply.
- Pop trailer supply valve, release tractor park brakes, ensure air pressure above 100 psi, shut down, pocket key, chock drive wheels, check drive axle slack adjusters.
- All done! Finish paperwork and drive!