Monaco Executive 2005 - Electric Thermovalve (ISX Engine); Switching Valve; Electric Override (ISM Only)

Chassis Information --- Section 10
The Executive 2005
505
Electric Thermovalve (ISX Engine)
The ISX engine uses an electric thermovalve to monitor two thermal sensors. One sensor is located
in the charge air pipe between the charge air cooler and intake manifold. If the intake air charge tem-
perature becomes too high, the hydraulic fans will engage to cool the charge air cooler. The other tem-
perature sensor monitors engine coolant. As coolant temperature increases, hydraulic fan speed will
commensurate with engine temperature. This method will use engine power sparingly to operate the
fans and keep the engine at the correct operating temperature.
Switching Valve
The switching valve is mounted to the fan motor and 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.
Electric Override (ISM only)
Motorhomes are equipped with an electric over hydraulic override control valve, located at the
lower rear corner of the radiator package. This valve is normally closed and is plumbed parallel with
the thermovalve and performs the same hydraulic signal function as the thermovalve, but electrically
controlled by the engine computer.
The engine computer monitors intake manifold temperature. The electronics of the engine control a
relay located in the rear run box. When intake manifold operating temperature is normal, the elec-
tronic engine will energize 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 engine electronics
detect an over temperature condition of the intake manifold, 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.