BENDIX FD-2 User Manual

®

Bendix® FD-2™ Clutch Type Fan Drive

SD-09-8503

FIGURE 1

SHAFT

BRACKET

AIR INLET

PULLEY

PRESSURE PLATEBEARINGS

DRIVE PIN

FAN HUB

RETURN SPRING

PISTON HOUSING
PISTON

BEARINGS

LOCK

NUT

DUST

CAP

FIGURE 2

DESCRIPTION

The Bendix® FD-2™ fan clutch is an air operated thermostat
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-2™ fan 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 for any cause.

OPERATION

GENERAL

The FD-2™ 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 5). The same valves used to control radiator
shutters are used to control the FD-2™ fan 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, the valve closes and exhausts air pressure from the
fan clutch which engages the fan.

1

FAN DISENGAGED

FIGURE 3

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.

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 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 4).

THERMO-PNEUMATIC

VALVE

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

FAN ENGAGED

FIGURE 5

BLOCK

THERMO-PNEUMATIC

VALVES

BLOCK

FAN

CLUTCH

FAN

CLUTCH

RADIATOR

RADIATOR

SHUTTER

FIGURE 4

2

FIGURE 6

AIR

CONDITIONING

SIGNAL

OVERRIDE

THERMO-PNEUMATIC

VALVE

FAN

SWITCH

AIR

CONDITIONING

OVERRIDE

SWITCH

RECEIVER

DRYER

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 full-open
temperature of the shutter.

SOLENOID

VALVE

BLOCK

FAN

FIGURE 7

AIR

CONDITIONING

SIGNAL

IGNITION

THERMO-PNEUMATIC

VALVES

BLOCK

AIR COND.

COMPRESSOR

FIGURE 8

AIR COND.

COMPRESSOR

SOLENOID VALVE

(NORMALLY OPEN)

FAN

CLUTCH

RADIATOR

CLUTCH

RADIATOR

FAN

OVERRIDE

SWITCH

CONDENSER

AIR

CONDITIONING

OVERRIDE

SWITCH

RECEIVER

DRYER

SHUTTER

CONDENSER

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

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 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. 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 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 electro­pneumatic override for the air conditioning. With this
combination the same requirements for fan control apply 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

Important: Review the warranty policy before performing

any intrusive maintenance procedures. An extended warranty
may be voided if intrusive maintenance is performed during

this period.
Because no two vehicles operate under identical conditions,

maintenance intervals will vary . Experience is a valuable guide
in determining the best maintenance interval for a vehicle.

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