Air Leakage Test; "Level-Low" Leveling System - Vip Series Option Only; Principles Of Operation; Maintenance - PREVOST H3-41 Maintenance Manual

7.3.2

Air leakage test

NOTE
The following procedure applies when valve
assembly has been removed from vehicle.
1. Clean the exterior of valve assembly.
2. Connect air pressure line to air inlet port,
then allow air pressure build-up (70- 100 psi
(480 - 690 kPa)).
3. Dip the valve assembly in a container full of
water, and watch for air bubbles when the
control arm is in the center position. No air
should escape from any point of the valve
assembly.
4. If bubbles appear from the air spring port,
this is an indication that the air inlet valve
assembly is defective and must be replaced.
5. Remove air pressure line from air inlet fitting
and connect it to the air spring port. If
bubbles appear at the air inlet check valve
port, this is an indication that the check valve
unit is defective and must be replaced.
6. If bubbles appear at the exhaust port, this is
an indication that
assembly is defective and must be replaced.
7. If bubbles appear around edge of valve
cover plate, the cover plate gasket must be
replaced.
8. If no leaks are found, remove valve
assembly from water, then with air pressure
still connected to the air spring port, actuate
control arm to remove any excess water
which may have entered exhaust valve
chamber. Remove air line, connect it to the
air inlet port, and repeat operation to remove
water from the air inlet valve chamber.
8 "LEVEL-LOW" LEVELING SYSTEM –
VIP SERIES OPTION ONLY
The purpose of the Level-Low leveling system is
to adjust suspension in three separate points
(front, rear right and rear left) in order to level
vehicle body. This system can be put into service
when the ignition key is turned to the "ON"
position, and must be used only when the
parking brake is applied. The Level-Low warning
light on the dashboard indicates that the selector
switch is not in the "OFF" position. Level low
system controls are located on L.H. side control
panel.
the exhaust valve
PA1621 Maintenance Manual All Series | Section revised October 2018
SECTION 16 : SUSPENSION
8.1

PRINCIPLES OF OPERATION

Down
The (front/rear right/rear left) control solenoid
valve supplies air to the (front/rear right/rear left)
five-way three-position air control valve, which
bypasses the (front/rear right/rear left) height
control valve, and opens a passage to allow the
air control and exhaust valve to release air from
(front/rear right/rear left) air springs.
Up
The (front/rear right/rear left) control solenoid
valve supplies air to the (front/rear right/rear left)
five-way three-position air control valve, which
bypasses the (front/rear right/rear left) height
control valve, and opens a passage to allow the
air control and exhaust valve to supply air to
(front/rear right/rear left) air springs.
Drive
When the ignition key is turned to the "ON"
position with selector knob in the "DRIVE"
position, the drive control solenoid valve supplies
air to all five-way three-position air control
valves, each one opening a passage to allow
height control valves
function.
When the ignition key is turned to the "OFF"
position and selector knob to the "DRIVE"
position, the air is entrapped between air springs
and five-way three-position air control valves to
ensure the adjusted level will be kept.
WARNING
Never move vehicle with selector knob in any
other position than the "DRIVE" position.
8.2

MAINTENANCE

Since the kneeling action is issued from both the
air system and electrical system, refer to
Section: 12, "Brake and Air System" and Section
06, "Electrical System".
For diagnosis and understanding of the system,
refer to wiring diagrams, and to the appropriate
air system schematic diagram annexed to
Section 12, "Brake and Air System".
to accomplish their
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