Navistar ProStar+, Operation And Maintenance Manual

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Operation
Air Compressor Cycling
The engines can be equipped with one of two different types of
air compressor and may have one or two cylinders.
• Head Unloaded Air Compressor: This single cylinder,
constantly engaged air compressor works in conjunction
with the air governor and air dryer to pump compressed
air to the air dryer and air tanks.
When additional
compressed air is not needed, air is shut off from the
air compressor discharge line and confined to the air
compressor cylinder and its head.
• Clutched Air Compressor: This high-capacity, two
cylinder, air compressor is periodically engaged by
using an On-Off clutch.
It works in conjunction with
air governor and air dryer to pump air to the air dryer
and air tanks. When additional compressed air is not
needed, the clutch is disengaged, compressor speed
goes to zero, and all air pumping ceases. This system
provides relatively low cylinder temperatures and sound
versus other compressors during the unloaded cycle. It is
used to promote maximum fuel economy by eliminating
pumping energy loss during the unloaded cycle.
As the compressor reaches approximately 130 psi (896 kPa),
the air governor will, through various methods, stop the air
compressor from pumping pressurized air to the air system.
When the air pressure reaches approximately 110 psi (758
kPa), the governor signals the air compressor to resume
pumping pressurized air to the air system.
During normal
engine operation, this cycle will be evident by the fluctuation of
the primary air tank pressure gauge.
Cooling System
WARNING
To prevent property damage, personal injury,
and / or death, use only the following procedure
to remove the pressure cap from the radiator
or expansion tank.
Allow the engine to cool
first. Wrap a thick, heavy cloth around the cap.
Unscrew the cap slowly to allow pressure to
release from under the cap. After the pressure
has been released, the pressure cap may be
removed.
WARNING
To prevent property damage, personal injury,
and / or death, exercise great care when working
on vehicles with running engines that are
equipped with an automatic fan clutch.
The
fan engages when engine coolant reaches a
predetermined temperature or the refrigerant
pressure (if equipped with air conditioning)
reaches a predetermined setting.
The fan will
start with no advance warning.
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