Switching Valve; Electric Override (Ism Engine); Fan Motor - Holiday Navigator 2003 Owner's Manual

Chassis Information
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Switching Valve

Electric Override
(ISM Engine)

Fan Motor

1 0 • 4 4 6
The switching valve is mounted to the fan motor. This valve controls
direction of high pressure hydraulic fluid flow. High pressure hydraulic fluid
comes from the hydraulic pump to the switching valve before returning to the
reservoir. Either the thermovalve or the electric override valve directs the fluid
to the spool in the switching valve. When the radiator is cool, pressurized
hydraulic fluid will bypass the fan motors and return to the fluid reservoir. As
radiator temperature rises, the thermovalve signal is slowed or stopped to the
switching valve. High pressure fluid is then directed to the fan motors, cooling
the radiator.
Motorhomes equipped with an ISM engine have an electric over hydraulic
override control valve. The override valve is located at the lower rear corner of
the radiator package. This valve is a normally closed valve which is plumbed
parallel with the thermovalve. It performs the same hydraulic signal function
as the thermovalve, but is electrically controlled by the ISM engine. The ISM
engine monitors intake manifold temperature. The electronics of the ISM
engine control an 87a relay located in the rear run box marked Hyd. Fans.
When intake manifold operating temperatures are normal, the electronic engine
energizes the coil of the relay. This energizes the coil of the override valve and
the hydraulic fluid signal flows through the override valve to the thermovalve.
If the ISM engine detects an over temperature condition of the intake man-
ifold, the coil of the 87a relay is deactivated. Power to the override valve is
removed, hydraulic fluid flow signal is stopped and internal spool of the
switching valve moves to full open position. The high pressure fluid is directed
to fan motors cooling the radiator.
The fan motors are driven by hydraulic fluid pressure from the switching
valve. The fan motors work on the same mechanical principal as a hydraulic
pump only the mechanical principal when applied to the fan motors is
reversed. Instead of creating hydraulic pressure by meshing gears together in a
close tolerance housing, the fan motors receive hydraulic pressure. The
hydraulic fluid drives the fan motor's internal gear assembly, spinning the fan
motors and the attached fan blades. The switching valve is mounted to one fan
motor. The fluid is directed to the input of that motor first. The output of the
first motor is hooked to the input of the second motor. The hydraulic fluid is
then cooled and filtered before returning to the reservoir.
N A V I G A T O R 2 0 0 3