Vehicles with dual air brake systems:
Have air pressure in the braking system even when the vehicle is not running.
Maintain some air pressure in the braking system when the vehicle is not running.
Must be run to build air pressure to allow the brakes to operate properly.
Maintain air pressure when shut off for periods of less than four hours.
Before driving a vehicle with a dual air brake system, allow time for the air compressor to build up pressure of at least 100 psi in both the primary and secondary systems.