Electromagnetic Fan Clutch Control, Function; Cooling Air Control, Function (With Code (M7K) Radiator Shutters) - Mercedes-Benz OM 471 Introduction Into Service Manual

Functions
i In vehicles with code (B3H) Secondary water retarder, during
the secondary water retarder's braking operation, the coolant
pump is actuated at full power to achieve a maximum braking
effect of the secondary water retarder.

Electromagnetic fan clutch control, function

The electromagnetic fan clutch delivery rate can be continuously
varied through the integrated electromagnetic viscous coupling.
The electromagnetic fan clutch is actuated by the engine
management (MCM) control unit (A4) using a PWM signal.
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Cooling air control, function (with code (M7K) Radiator shutters)

The lower radiator shutters control unit (A54) and the upper
radiator shutters control unit (A55) is actuated steplessly by the
drive control (CPC) control unit (A3) over the radiator shutters LIN
(LIN 5). The radiator shutters are opened and closed as a function
of the following factors:
Secondary water retarder operating condition
f
(with code (B3H) Secondary water retarder)
f Engine brake operating condition
f A/C operating condition
f Heat output requirement
f Vehicle speed
f Outside air temperature
f Coolant temperature
f Boost air temperature
f Engine speed
Vehicle operating condition
Ignition OFF,
Parking brake closed
Engine running,
Parking brake open
Vehicle accelerates,
Vehicle speed 55 km/h
Speed 55 km/h,
No cooling request pending
Speed drops below 55 km/h,
Cooling request pending
Vehicle speed 20 km/h
Air conditioning switched on
Secondary water retarder in braking
operation
(With code (B3H) Secondary water retarder);
Coolant temperature < 94 ∞C and brake
power < 150 kW
Secondary water retarder in braking
operation
(With code (B3H) Secondary water retarder);
Coolant temperature < 94 ∞C and brake
power > 150 kW
88
Upper radiator shutters
Is opened and remains open
Opens 5 s after braking of secondary water
Opens immediately
– This printout will not be recorded by the update service. Status: 09 / 2011 –
The engine management (MCM) control unit (A4) evaluates the
following information for this:
f Coolant temperature
f Engine oil temperature
f Boost air temperature
f Engine speed
f Fan speed
f Secondary water retarder operating condition
(with code (B3H) Secondary water retarder)
Depending on the listed information, the engine management
(MCM) control unit (A4) calculates the set value for actuation of
the electromagnetic fan clutch.
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Depending on the listed information, the drive control (CPC)
control unit (A3) uses a characteristics map to calculate the set
values for actuation of the radiator shutters.
i To prevent any repeated radiator shutter switching, there is a
hysteresis between the opening and closing points.
This means that the opening time of the radiator shutters is
30 s, even when the vehicle's operating condition would result in
the corresponding radiator shutters being closed.
The lower radiator shutters control unit (A54) and the upper
radiator shutters control unit (A55) closes or opens the slats as
described in the following table:
Open
Open
Open
Closed
Open
Open
retarder starts
Lower radiator shutters
Closed (step protection)
Open
Open
Closed
Is opened and remains open
Open
Open
Opens 5 s after braking of secondary water
retarder starts
Opens immediately