Air Horn Valve; Air System Troubleshooting; Brake Operation - PREVOST H3-41 Maintenance Manual

1. Unscrew the front R.H. decorative panel in
order to access the valve.
2. Unscrew and remove the valve handle.
3. Unscrew and remove the valve retaining
ring.
4. Push the valve inside the console.
5. Disconnect the air tubes.
6. Reverse the procedure to install a new
valve.

15. AIR HORN VALVE

The air horn solenoid valve is located in the front
service compartment. The air horn activating
button is on the center of the steering wheel.
Refer to section 23 "ACCESSORIES" for more
information.

16. AIR SYSTEM TROUBLESHOOTING

The following list has been designed to help in
troubleshooting some of the most common
problems in the air system and main causes. For
air brakes troubleshooting, refer to "Air Brakes
Troubleshooting" in this section. For more
troubleshooting information,
manufacturer's brochures,
Technical Publications USB flash drive.
Air pressure doesn't rise to or doesn't
maintain a normal setting:
• Defective air gauge (registering incorrectly).
• Excessive leaking in air system.
• Reservoir drain cock open.
• Governor poorly adjusted or defective.
• Defective compressor.
• Worn compressor or excessive wear on
piston and/or ring.
Air pressure rises to normal setting too
slowly:
• Excessive leaking in air system.
• Clogged engine air cleaner.
• Faulty pressure sensor.
• Worn compressor or excessive wear on
piston and/or ring.
refer to the
found on your
PA1621 Maintenance Manual All Series | Revised June 2020
SECTION 12: BRAKE AND AIR SYSTEM
• Engine speed too low.
Air pressure rises above a normal setting:
• Defective air gauge (registering incorrectly).
• Faulty sensor.
• Restriction in line between governor and
compressor unloading mechanism.
• Air filter/dryer built-in
adjusted or defective.
Air pressure drops quickly when engine is
stopped:
• Leaks in compressor discharge valve.
• Leaks in air lines.
• Leaks in air system valves.

17. BRAKE OPERATION

The vehicle braking system uses both service
and parking air-operated brakes. The air system
is divided into two independent circuits to isolate
the front axle brakes and the rear axle brakes
(drive and tag), thus providing safe brake
operation in the event that one circuit of the
system fails. The primary circuit is connected to
the drive and tag axle brakes, while the
secondary circuit is connected to the front axle
brakes. The tag axle service brakes operate only
when the axle is in the normal driving (loaded)
position. The spring-type emergency brakes are
mounted on the drive and tag axles, and will
apply automatically if primary system pressure
falls below 60 psi (413 kPa).
The optional parking brake override system can
cancel the parking brakes, enabling the driver to
move the vehicle to a safe parking place. On
vehicles equipped with this option, operate the
system by pushing down and holding the control
knob located on the R.H. side of the driver's seat
(see "Operator's Manual" for more details).
Furthermore, brake application or release, which
is sped up by a pneumatic relay valve (R-14), will
start with the rear axles and be followed by the
front axle, thus providing uniform braking on a
slippery surface. The vehicle is also equipped
with an Anti-lock Brake System (ABS), detailed
later in this section.
Brake and air system maintenance consists of
periodic inspections. Check all parts for damage
governor poorly
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