Description of Components
DESCRIPTION OF COMPONENTSFor the location image of the components listed below refer to Locations/Components/Locations of Components Locations
Electrical control unit - ECU
The ECU is located underneath the right hand front seat, on top of the fuel ECU. It maintains the requested vehicle ride height by adjusting the volume of air in each air spring. It is connected to the cable assembly by a 35 way connector. To ensure safe operation the ECU has extensive on board diagnostic and safety features. The ECU is non-serviceable, in case of failure it must be replaced.
Relays, fuses
Power supply for the system consists of the following components:
1. Delayed power turn off relay. This remains powered up for 20 seconds after exiting vehicle to allow self levelling.
2. Compressor relay, 4 pin.
3. Warning light relay, 5 pin.
4. 30 amp 'maxifuse' for compressor power.
5. 15amp fuse for ECU pin 1.
Disable switch
The disable switch 6. is mounted under the right hand front seat. The switch has no markings, in the DISABLE position the bottom of the switch is pushed in. It is used to disable system when vehicle is being delivered, or when working on the system after depressurizing. The switch disables the system at speeds below 56 kph (35 mph).
Height sensors
Four potentiometer type height sensors signal vehicle height information to the ECU. The potentiometers are mounted on the chassis and activated by links to the front radius arms and rear trailing links. In case of height sensor failure the assembly must be replaced.
Control switches
Mounted on the lower dash, three control switches are arranged thus:
1. Raise - momentary touch switch.
2. Inhibit - self latching switch, when switched on the vehicle will remain at standard ride height. This position is used when the automatic height adjustment is not required i.e. when towing. Self levelling will continue to function.
3. Lower - momentary touch switch.
The switches incorporate a warning lamp. When engine is started all three warning lamps will illuminate for three seconds as part of bulb check. The switches are illuminated when the vehicle lights are on, controlled by the dimmer switch.
The following components, AIR COMPRESSOR, AIR DRYER and VALVE BLOCK are contained in the AIR SUPPLY UNIT mounted on the right hand chassis side.
Air compressor
The air compressor provides system pressure. A thermal switch is incorporated which switches off the compressor relay ground at 130°C. The compressor has an air intake silencer mounted behind rear mud flap. The air intake filter is located adjacent to the fuel filler flap. The filter is renewed every 40,000 kms/24,000 miles/24 months. (30,000 miles USA).
Air dryer
The air dryer is connected into the air line between compressor and reservoir. It removes moisture from pressurized air entering the system. When air is exhausted from the system it passes through the dryer in the opposite direction. The air dryer is regenerative in that air absorbs moisture in the dryer and expels it to atmosphere.
The air dryer unit is non-serviceable, designed to last the life of the vehicle. However if water is found in the system when reservoir drain plug is removed, the air dryer must be changed.
CAUTION: If the air dryer is removed from the vehicle the ports must be plugged to prevent moisture ingress.
Valve block
The valve block controls the direction of air flow. Air flow to and from the air springs is controlled by six solenoid operated valves, one for each air spring, one inlet and one exhaust. A diaphragm valve operated by the solenoid outlet valve ensures that all exhausted air passes through the air dryer. In response to signals by the ECU, the valves allow high pressure air to flow in or out of the air springs according to the need to increase or decrease pressure. The valve block is non-serviceable, in case of failure it must be replaced.
Non-return valves
The valve block contains three non-return valves. NRV1 retains compressor air pressure by preventing flow back to the compressor.
NRV2 prevents loss of pressure in the system if reservoir pressure drops. It also ensures correct flow through the inlet valve.
NRV3 ensures correct flow through the exhaust valve.
Reservoir
The 10 litre reservoir is mounted on the left hand side of the chassis. One connection acts as inlet and outlet to the rest of the system. It stores compressed air between set pressure levels. The reservoir drain plug requires removing every 40,000 kmsl24,000 miles/24 months. (30,000 miles USA) to check for moisture in the system, refer to Accumulator (Oil/Air For Level Control)/Service and Repair/Air Reservoir, Draining Service and Repair
Pressure switch
Mounted on the reservoir is a pressure switch which senses air pressure and signals the ECU to operate the compressor when required. The compressor will operate when pressure tails to between 7.2 and 8.0 bar (104 and 116 psi). It will cut out at a rising pressure of between 9.5 and 10.5 bar (138 and 152 psi).
Air springs
Air spring components:
1. Top plate
2. Rolling rubber diaphragm
3. Piston
The air springs are mounted in the same position as conventional coil springs.
Front and back air springs are of similar construction, but are not interchangeable.
The diaphragm is NOT repairable, if failure occurs the complete unit must be replaced.