BENDIX FD-1 User Manual

®

Bendix® FD-1™ Clutch Type Fan Drive

SD-09-8501

FIGURE 1

O-RING

BRACKET

TEFLON
BACK-UP

RING

AIR PASSAGE

SHAFT

GREASE

PASSAGE

GREASE
FITTING

SPACER

AIR INLET

BEARINGS

PULLEY

RETAINER NUT

PISTON

PRESSURE

PLATE

BEARING

RETAINER

DOUBLE ROW
BALL BEARING

FAN PILOT

SPRING

CAGE

SPRING

FAN

FRICTION
MATERIAL

FIGURE 2

DESCRIPTION

The Bendix® FD-1™ fan clutch is a pneumatically operated,
thermostatically controlled clutch for the engine cooling fan.
Its purpose is to maintain engine temperature by engaging
or disengaging the cooling fan, thereby providing better
fuel economy , greater engine efficiency , faster warm-ups and
a quieter vehicle.

The FD-1™ clutch is produced in several different models to
accommodate the variety of installation requirements
resulting from the many engine, vehicle and accessory
combinations. Its fail-safe design prevents overheating in
the event of air loss or component or air line failure.

OPERATION

GENERAL

The FD-1™ fan clutch replaces the standard fan hub on the
engine and is controlled by a temperature sensitive air valve
(see Fig. 5). The same valves used to control radiator
shutters are used to control the FD-1™ clutch. 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, it closes and exhausts air pressure from the fan
clutch which engages the fan.

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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.

FAN DISENGAGED

FIGURE 3

ENGAGED

As the engine coolant rises in temperature, the engine
thermostat opens to circulate radiator coolant through the
engine. With further increase in coolant temperature, the
fan drive control valve closes and exhausts air from the
piston cavity when the engine coolant temperature reaches
the setting of the control valve. The fan clutch spring forces
the piston and pressure plate back on the shaft. When the
pressure plate lining contacts the pulley , the fan is engaged
and is driven by the engine (see Fig. 4).

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 5. Fan Clutch only
Figure 6. Fan Clutch with shutters
Figure 7. Fan Clutch with radiator mounted air

conditioning condenser

Figure 8. Fan Clutch, shutters and condenser

FAN ENGAGED

FIGURE 4

DISENGAGED

When the vehicle is started with a cold engine the thermo­pneumatic 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 and fan to the
disengaged position. In this position the clutch lining is out
of contact with the pulley and the fan is no longer driven by
the engine (see Fig. 3).

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 full open point
of the engine thermostat.

The objective in the case of Figure 6 is to not engage the
fan until the shutters are fully open. The fan control valve
should, therefore, engage the fan at a coolant temperature
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 7 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 7. When
this pressure switch senses a higher than normal pressure
in the air conditioning system (approximately 250 P .S.I.), it
closes an electrical circuit which in turn energizes a solenoid
operated air supply valve which exhausts the air supply for

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THERMO-PNEUMATIC

VALVE

AIR

CONDITIONING

SIGNAL

THERMO-PNEUMATIC

VALVE

FAN

OVERRIDE

SWITCH

AIR

CONDITIONING

OVERRIDE

SWITCH

RECEIVER

DRYER

BLOCK

FAN

CLUTCH

RADIATOR

FIGURE 5 FIGURE 7

CONDITIONING

THERMO-PNEUMATIC

VALVES

BLOCK

FAN

CLUTCH

RADIATOR

SHUTTER

SIGNAL

THERMO-PNEUMATIC

BLOCK

AIR COND.

COMPRESSOR

AIR

(NORMALLY OPEN)

VALVES

BLOCK

AIR COND.

COMPRESSOR

SOLENOID

VALVE

CLUTCH

SOLENOID VALVE

FAN

CLUTCH

RADIATOR

FAN

RADIATOR

FAN

OVERRIDE

SWITCH

CONDENSER

AIR

CONDITIONING

OVERRIDE

SWITCH

RECEIVER

DRYER

SHUTTER

CONDENSER

the fan control, causing the fan to engage. 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 P.S.I.
and opens again at approximately 400 P.S.I. 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 P.S.I.). This switch does not normally
have anything to do with fan operation; however, it is
sometimes combined with the previously mentioned override
switch.

Figure 8 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

FIGURE 8FIGURE 6

as in Figure 6 and 7 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

The durability of the Bendix® FD-1™ fan clutch matches that
of the vehicle’s engine when proper maintenance is
performed. Maintenance intervals for the FD-1™ clutch will
vary in relation to the type of service the vehicle performs.
The following is a guide:

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