BENDIX FD-3 User Manual

®

Bendix® FD-3™ TorqueMaster Fan Clutch

SD-09-8504

BRACKET

PULLEY

SHAFT

BRACKET

FAN PLATE

DUST

CAP

BEARINGS

PRESSURE PLATE

RETURN SPRINGS (8)

FAN HUB

PISTON

BEARINGS

LOCK NUT

DUST

CAP

PILOT DIAMETER

2.560

PISTON HOUSING

BEARINGS

LOCK

NUT

AIR INLET

PULLEY

FIGURE 1

DESCRIPTION

The Bendix® FD-3™ T orqueMaster fan clutch is an air operated
thermostat controlled clutch for the engine cooling fan. Its
purpose is to maintain engine temperature by engaging or

O-RINGS

DUST

STANDARD PILOT

DIAMETER 1.998

DRIVE PIN (2)

CAP

disengaging the cooling fan, thereby providing better fuel
economy , greater engine efficiency , faster warm-ups and a
quieter vehicle.

The FD-3™ fan clutch is produced in several different models
to accommodate the variety of installation requirements

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resulting from the many engine, vehicle and accessory
combinations. Its fail-safe design prevents overheating in
the event of air loss for any cause.

FAN ENGAGED

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
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, dif ferent piping arrangements are
necessary. These will be explained in the paragraph on
control systems.

™

T orqueMaster. Installed in the engine block, the

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).

FAN DISENGAGED

PISTON SHOULD

MOVE FORWARD AS

AIR IS EXHAUSTED

FIGURE 3

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. F AN CLUTCH ONL Y
FIGURE 5. F AN CLUTCH WITH SHUTTERS
FIGURE 6. FAN CLUTCH WITH RADIATOR MOUNTED

CONDITIONING CONDENSER

FIGURE 7. F AN 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 thermo­pneumatic 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 full­open temperature of the shutter.

FIGURE 2

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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

and low road speed or idling. If the condenser is inadequately
cooled, the air conditioning system will start to build up a
higher than normal pressure. Therefore, a pressure switch
is connected into the air conditioning compressor discharge
line, as shown in Figure 6. When this pressure switch senses
a higher than normal pressure in the air conditioning system
(approximately 250 psi), it closes an electrical circuit which
in turn energizes a solenoid operated air supply valve which
exhausts the air supply for the fan control, causing the fan
to engage.

THERMO-PNEUMATIC

VALVE

AIR

CONDITIONING

SIGNAL

SOLENOID VALVES
(NORMALLY OPEN)

IGNITION

THERMO-PNEUMATIC

VALVE

BLOCK

AIR COND. COMPRESSOR

OVERRIDE

SWITCH

FAN

CLUTCH

FAN

AIR

CONDITIONER

OVERRIDE

SWITCH

RECEIVER

DRYER

FIGURE 4

FIGURE 5

AIR

CONDITIONING

SIGNAL

THERMO-PNEUMATIC

BLOCK

THERMO-PNEUMATIC

VALVES

BLOCK

FAN

CLUTCH

RADIATOR

VALVE

FAN

CLUTCH

RADIATOR

FAN

OVERRIDE

SWITCH

SHUTTER

AIR

CONDITIONING

OVERRIDE

SWITCH

RECEIVER

DRYER

SHUTTER

FIGURE 7

RADIATOR

CONDENSER

Most vehicles also have an additional dual function pressure
switch connected in series with the air conditioner clutch.
This switch is normally open, closes at approximately 30
psi and opens again at approximately 400 psi. Its purpose
is to prevent operation of the air conditioning compressor if
the refrigerant is lost or to shut off the compressor if the
system pressure reaches a dangerously high pressure
(approximately 400 psi). This switch does not normally have
anything to do with fan operation; however, it is sometimes
combined with the previously mentioned override switch.

Figure 7 depicts a combination of shutters, fan clutch and
air conditioning. This combination requires the two thermo­pneumatic controls for fan and shutters, as well as the
electro-pneumatic override for the air conditioning. With
this combination the same requirements for fan control apply
as in Figure 5 and 6 with the additional requirement that the
shutters should be controlled in such a manner that they
always open whenever the air conditioning compressor
operates.

A variation of this combination consists of a two section
shutter with one section in front of the condenser and the
other in front of the remaining portion of the radiator. In this
combination only the section in front of the condenser needs
to open when the air conditioner engages.

PREVENTIVE MAINTENANCE

SOLENOID VALVE

BLOCK

AIR COND.

COMPRESSOR

FAN

CLUTCH

RADIATOR

FIGURE 6

CONDENSER

There is no need for periodic maintenance; however, the
following service checks should be made to ensure proper
function of the fan clutch.

GENERAL

The condition of the two fan plate ball bearings should be
checked at regular intervals to ensure proper operation of
the FD-3™ fan clutch. The procedure presented here is
intended to check excessive bearing play by measuring

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