From the service information on TechConnect.
DESCRIPTION
WARNING:
All pressurized air suspension components contain high pressure air (up to 220 psig). Use extreme caution when inspecting for leaks. Wear safety goggles and adequate protective clothing when inspecting or servicing the air suspension system. A sudden release of air under this amount of pressure can cause possible serious or fatal injury.
WARNING:
Support the vehicle by supplemental means before performing any work on the air suspension system to prevent the vehicle from changing height. Before any given component is to be serviced it must be deflated. Servicing the air suspension system without supplemental support, or with pressure in the specific component, can cause possible serious or fatal injury.
CAUTION:
When handling the air suspension compressor assembly, keep upright and carry only by the compressor itself or the primary bracket (bolts the assembly to the vehicle).
The Air Supply Unit (ASU) is located on the vehicle frame rail on the passenger side of the vehicle. The ASU contains the air dryer, compressor, exhaust valve, valve block, pressure sensor, and temperature sensor.
The compressor itself is suspended from the ASU mounting bracket by three spring loaded studs to reduce vibration and noise. The valve block is bolted to a mounting bracket that is in turn bolted directly to the side of the ASU mounting bracket. The ASU is serviced as an assembly.
The compressor cannot refill the reservoir and the complete system if all pressure is exhausted, as in a compressor assembly or valve block replacement. The system will need to be filled at the reservoir with nitrogen. For complete filling of the air suspension system after a repair (Refer to 17 - Rear Suspension/Standard Procedure) .
Complete filling procedure
This procedure should only be necessary when the entire system was purged of air, such as the replacement of the compressor or valve block assembly.
NOTE:
The gauge (1) on Air Suspension Refill Tool - Tool, Air Suspension Refill 10247B reads the tank pressure. The regulator limits the pressure in the line (4) to 12 bar (175 psi). When connected to the reservoir with the valves open, pressure in the reservoir can be read on the scan tool.
The Air Suspension Refill Tool - Tool, Air Suspension Refill 10247B (1, 4 ,5 ,6) is used with a nitrogen supply tank (2, 3) which can be acquired at a local gas supplier. The nitrogen must be Purity Class 5 (99.999% pure).
1.Raise and support the vehicle so the suspension system is hanging (all four wheels off the ground) (Refer to 04 - Vehicle Quick Reference/Hoisting - Standard Procedure) .
2.Make sure the Air Suspension Refill Tool - Tool, Air Suspension Refill 10247B line on/off valve (6) is turned off and the nitrogen tank valve is turned off (2).
NOTE:
The fill fitting on the air suspension reservoir is located under the passenger side of the cab, on the frame rail,
3.Remove the reservoir fill connection cap (not shown).
4.With Air Suspension Refill Tool - Tool, Air Suspension Refill 10247B (1, 2, 5) attached to a nitrogen tank, connect the quick coupler (2) to the air suspension reservoir fill connection (3) and open the valve (1) by turning clockwise.
NOTE:
The regulator on Air Suspension Refill Tool - Tool, Air Suspension Refill 10247B
is preset to 12 bar (175 psi) (as read with a scan tool, the gauge reads tank pressure only). When connected to the reservoir and the valves open, the pressure will equalize to 12 bar (175 psi) in approximately 10-15 seconds. A hissing sound can be heard while the nitrogen is being transferred and the sound will stop when the pressures are equalized.
Fill the reservoir to approximately 12 bar (175 psi) by fully opening the valve (2) on the nitrogen tank (3) and the valve (6) on Air Suspension Refill Tool - Tool, Air Suspension Refill 10247B (1, 4 ,5 ,6).
6.When the pressures are equalized, close the valve (6) on the tool.
7.Take measurements of the component air mass, pressure and the ride height readings.
8.With a scan tool, perform a Short Fill on one rear air spring, then a short fill on the other air spring.
NOTE:
Verify that the air springs are seated properly.
Using a scan tool, use the routines under the Air Suspension Control Module (ASCM), carry out air filling via reservoir to fill both air springs .
10.Fill the reservoir again by repeating steps 6 and 7.
11.With a scan tool, using the routines under the Air Suspension Control Module (ASCM), perform a Complete Fill on each rear spring assembly.
12.Verify the Air Suspension Refill Tool - Tool, Air Suspension Refill 10247B line on/off valve (6) is closed and close and the nitrogen tank valve (2).
13.Remove the supports and lower the vehicle.
14.Close the valve (1) by turning counter clockwise, remove the quick coupler (2) from the air suspension reservoir fill connection (3) and install the reservoir fill connection cap (not shown).
15.With a scan tool, using the routines under the Air Suspension Control Module (ASCM), perform the following:
•Command the vehicle to Normal Ride Height.
•Run the Air Mass Calculation routine on the air suspension system.
•If necessary, add to the system or deflate to atmosphere using the ASCM routines, then repeat the Air Mass Calculation routine again until system responds with Air Mass OK (188 - 216 bar-liters).
16.Perform the ASCM Verification Test .
Attention: TDR Forum Junkies 
