2
FIGURE 3
FAN DISENGAGED
FIGURE 2
FAN ENGAGED
resulting from the many engine, vehicle and accessory
combinations. Its fail-safe design prevents overheating in
the event of air loss for any cause.
OPERATION
GENERAL
The FD-3
™
TorqueMaster fan clutch replaces the standard
fan hubs on the engine and interchanges with other Bendix
and competitive fan clutches. It is controlled by a
temperature sensitive air valve. (See Figure 4). The same
valves used to control radiator shutters are used to control
the FD-3
™
TorqueMaster. Installed in the engine block, the
control valve directly senses coolant temperature. Provided
coolant temperature remains below the setting of the valve,
air passes through it to disengage the fan clutch. When
coolant temperature rises to the valve setting, the valve
closes and exhausts air pressure from the fan clutch which
engages the fan.
Depending upon optional equipment installed on the vehicle
such as radiator shutters and radiator mounted air
conditioning condenser, different piping arrangements are
necessary. These will be explained in the paragraph on
control systems.
DISENGAGED
When the vehicle is started with a cold engine the
thermo-pneumatic control valve is open. As brake system
air pressure is built up, air passes through the control valve
to the fan clutch. Air enters the inlet port in the bracket of
the fan clutch and travels through the drilled passage in the
shaft to fill the piston cavity. When air in the piston cavity
reaches a pressure of 70-75 psi, the piston slides on the
shaft moving the pressure plate assembly to the disengaged
position. In this position the clutch lining is out of contact
with the fan plate and the fan is no longer driven by the
engine (see Fig. 2).
ENGAGED
As the engine coolant rises in temperature, the engine
thermostat opens to circulate radiator coolant through the
engine. When the engine coolant temperature reaches the
setting of the control valve, the valve exhausts air from the
piston cavity. The fan clutch springs force the piston and
pressure plate forward on the shaft. When the lining
contacts the fan plate, the fan is engaged and is driven by
the engine (see Figure 3).
CONTROL SYSTEMS
The fan clutch, in addition to its primary function of operating
the fan as needed to maintain the cooling liquid within a
certain temperature range, must be coordinated with other
devices when installed on the vehicle.
These are radiator shutters and radiator mounted condenser
for air conditioning. Four basic configurations are possible
as follows:
FIGURE 4. FAN CLUTCH ONLY
FIGURE 5. FAN CLUTCH WITH SHUTTERS
FIGURE 6. FAN CLUTCH WITH RADIATOR MOUNTED
CONDITIONING CONDENSER
FIGURE 7. FAN CLUTCH, SHUTTERS AND CONDENSER
The objective in the case of Figure 5 is to not engage the fan
until the engine thermostat is fully open. The thermo-
pneumatic control valve should therefore be calibrated to
release the air from the fan clutch when the coolant
temperature is at least 10°F higher than the shutter opening
point. If the shutters are the modulating type, the fan
engagement should be at least 10°F higher than the full-
open temperature of the shutter.
In the case of Figure 6 the fan must be controlled to perform
the supplementary function of pulling cooling air through
the air conditioning condenser when required, although the
engine coolant may be below the fan cut-in temperature.
This is most likely to occur at high ambient temperatures
PISTON SHOULD
MOVE FORWARD AS
AIR IS EXHAUSTED