2
FIGURE 3
FIGURE 5
FAN DISENGAGED
FIGURE 4
FAN ENGAGED
FIGURE 6
THERMO-PNEUMATIC
VALVE
THERMO-PNEUMATIC
VALVES
BLOCK
FAN
CLUTCH
RADIATOR
RADIATOR
FAN
CLUTCH
BLOCK
SHUTTER
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 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).
