Section 10 --- Chassis Information
The Executive 2005
504
Hydraulic Fan System
The hydraulic fan drive system cools the radiator, charge air cooler, hydraulic fluid cooler, trans-
mission cooler and the dash air conditioning condenser. The components of the hydraulic fan system
are: hydraulic reservoir, filter, pump, hydraulic fan motor(s), hydraulic switching valve and thermovalve.
Cooling fan speed is proportional to engine speed and coolant temperature. When coolant temperature rises
above 185º F, the thermovalve slowly closes off the bypassing hydraulic fluid from the switching
valve. As coolant temperature rises, a spool valve begins to move in the switching valve. The spool
valve directs the pressurized hydraulic fluid to the fan motors. The higher the coolant temperature, the
further the spool valve is moved in the switching valve, providing a higher volume of pressurized
hydraulic fluid to the fan motors. Fan motor speed is increased to meet the demand for cooling. The
action of the thermovalve is designed to move the spool in the switching valve to ramp up fan motor
speed. This design saves horsepower and increases fuel mileage by precise control of hydraulic fan
motor speed. The fan motors will increase in speed when the motorhome is ascending long hills or
operating in high ambient temperatures. It is normal for the fans to "roar" when they are operating.
Fan motor speed and engine RPM are approximately the same with the switching valve at full engage-
ment.
Thermovalve (ISM & Series 60 Engines)
The wax filled thermovalve, mounted at the top of the radiator, controls the action of the switching
valve. When the radiator is cool, hydraulic fluid is allowed to flow through the inlet and outlet ports of
the thermovalve and return to the hydraulic reservoir. As coolant temperature inside the radiator rises to
approximately 185º F, wax inside the thermovalve begins to melt and expand, which restricts hydraulic
fluid flow through the thermovalve. The restricted hydraulic fluid pressure then begins to move the
internal spool valve of the switching valve. This process will continue until coolant temperature
inside the radiator reaches approximately 199º F. At this temperature, hydraulic fluid flow through
the thermovalve is stopped, moving the spool valve to full open position.
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