Variable Speed Cooling Fan; Locking Radiator Fan Clutch For Emergency Operation; Electrical Locking; Mechanical Locking In Case Of Power Failure - PREVOST H3-41 Maintenance Manual

4. Bolt the new idler on the cast aluminum
support.
TORQUE: 32 lb-ft (43 Nm)
5. Place a new protective cap.

14. VARIABLE SPEED COOLING FAN

The cooling fan clutch has two thermostatically
controlled speeds, plus
disengaged). The engine control module controls
the speed by comparing data from engine
coolant temperature, charge air temperature,
Allison transmission oil temperature and small
A/C high side pressure to a set of calibration
data. The fan drive clutch is electromagnetic;
the engine control module sends an electric
current to regulate speed by activating one
magnetic coil for the first speed and two
magnetic coils for the second speed.
The settings are:
Engine
coolant
temp.
temperature 208°F: fan
rising engages in
HIGH
SPEED
203°F: fan
engages in
LOW
SPEED
temperature 203°F: fan
dropping HIGH
SPEED
disengages
198°F: fan
LOW
SPEED
disengages
Small A/C high side pressure
pressure rising
170 psi: fan engages in HIGH
SPEED
120 psi: fan engages in LOW
SPEED
pressure dropping 130
disengages
90
disengages
a neutral (clutch
Air intake Allison
temp. trans. oil
temp.
194°F: fan 230°F: fan
engages in engages in
HIGH HIGH
SPEED SPEED
176°F: fan 216°F: fan
engages in engages in
LOW LOW
SPEED SPEED
189°F: fan 225°F: fan
HIGH HIGH
SPEED SPEED
disengages disengages
170°F: fan 210°F: fan
LOW LOW
SPEED SPEED
disengages disengages
psi: fan HIGH SPEED
psi: fan LOW SPEED
PA1615 Maintenance Manual All Series
SECTION 05b: X3 SERIES COOLING SYSTEM
WARNING
DO NOT work near the fan with the engine
running or the ignition in the ON position. The
engine fan can engage at any time without
warning. Anyone near the fan when it turns on
could be seriously injured.
14.1 LOCKING RADIATOR FAN CLUTCH FOR
EMERGENCY OPERATION

14.1.1 Electrical Locking

If the radiator fan clutch does not function due to
an electrical control system malfunction and the
engine is overheating, you can activate the fan
clutch through one of the Driver Information
Display menus. For more detail, refer to "Forced
Activation of the Radiator Fan Clutch" paragraph
in Section 06: ELECTRICAL.
NOTE
If the fan clutch does not engage using this
procedure then the clutch is faulty or the wiring
between the multiplex module and the clutch is
faulty. Mechanically lock the fan as described
in section 13.1.2.
14.1.2 Mechanical Locking In Case Of Power
Failure
Once mechanically locked, the fan clutch is
rigidly connected to the drive mechanism and will
rotate continuously, with no considerations for
the cooling needs. This is an emergency
situation and the vehicle shall not be operated in
that situation for an extended period.
In case of a magnetic clutch malfunction:
1. Set the ignition to the OFF position and
remove the key from the contact switch to
prevent accidental starting of the engine.
2. Disconnect the
connector.
3. Unscrew and remove the 4 spare M6x12 hex
bolts screwed to the angle on the fan gearbox
mounting support (
4. Screw in 4 hex bolts through the clutch
anchor plate into the rotor. Using the
automatic belt tensioner, release tension on
the drive belt in order to be able to rotate the
fan clutch drive mechanism by hand.
TORQUE: 7.5 lb-ft (10 Nm)
|
Section 05b revised September 2016
fan clutch electrical
).
FIGURE 24
23