• Steering flow control valve
• Fan control valve
• Two stage G-rotor hydraulic drive
The hydraulic fan and drive are not serviceable.
Any failure of the fan blade, hydraulic fan drive or
fan shroud requires replacement of the fan module.
The fan blade and hydraulic fan drive are matched
and balanced as a system and servicing either sepa-
rately would disrupt this balance.
For hydraulic fluid routing information refer to
(Fig. 8).
CAUTION: Do not attempt to service the hydraulic
cooling fan or fan drive separately replace the cool-
ing module as an assembly. Failure to do so may
cause severe damage to the hydraulic cooling fan
assembly.
OPERATION
The hydraulic radiator cooling fan replaces both
the electric fan and the engine driven mechanical
fan. The use of this hydraulic fan provides heavy
trailer tow capability while at the same time reduc-
ing unnecessary power drain on both the engine and
the vehicles electrical system.
HYDRAULIC FAN STRATEGY
The hydraulic radiator cooling fan is controlled by
the Electronic Control Module (ECM). A PWM (Pulse
Width Modulated) signal from the ECM controls the
fan from 0 to 100% of the available fan speed. There
are four inputs to the ECM that determine what
speed percentage of fan is required by the vehicle.
These inputs are:
• Engine Coolant Temperature
• Transmission Oil Temperature
• Battery Temperature
• A/C System Pressure
By monitoring these four parameters, the ECM can
determine if cooling airflow is required. If airflow is
required, the ECM will slowly ramp up (speed up)
the fan speed until the operating parameter(s) are
met for the driving condition. Once the temperature
or pressure is reduced to within operating parame-
ters, the fan will adjust or hold its speed to maintain
the temperature / pressure requirements.
NOTE: If the ECM is not requesting fan on opera-
tion, the fan blade will spin between 100 and 500
RPM when the vehicle is at idle. This is due to a
controlled minimum oil flow requirement through
the fan drive motor.
ACTIVATING THE HYDRAULIC FAN WITH THE
DRBIIIT
Under the Engine Systems test heading, there is a
subheading. “Hydraulic fan solenoid test”, that has
the selections, on /off. Activating the fan with the
DRBIIIt will run the fan at 100% duty cycle, which
will help troubleshoot any system problems, and also
help with the deaeration procedure.
NOTE: Engine must be running to activate the fan
with the DRBIIIT.
RADIATOR COOLING FAN HYDRAULIC FLUID PATH
Hydraulic fluid is pumped from the power steering
pump, though a high pressure delivery line, to the
fan drive motor. As fluid is diverted through the
G-rotors, rotational motion moves fluid from the
high-pressure (inlet) side of the motor to the low-
pressure (outlet) side. Fluid exiting the drive motor
is divided into two paths. Path one continues through
a high pressure delivery line to the steering gear,
and path two sends fluid back to the power steering
pump through a low pressure line. Fluid exits the
steering gear under low pressure and travels through
a low pressure line to the power steering fluid cooler
before being returned back the power steering fluid
reservoir (Fig. 7).
Fig. 7 HYDRAULIC RADIATOR COOLING FAN AND
FAN DRIVE
1 - POWER STEERING FLUID COOLER
2 - RADIATOR
3 - HIGH PRESSURE LINE FROM STEERING GEAR PUMP TO
HYDRAULIC FAN MOTOR
4 - HYDRAULIC FAN MOTOR
5 - HIGH PRESSURE LINE FROM HYDRAULIC FAN MOTOR TO
STEERING GEAR
6 - FAN SHROUD
7a - 16 ENGINE WG
RADIATOR FAN (Continued)
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