3
FIGURE 5
FIGURE 7
FIGURE 6
FIGURE 4
THERMO-PNEUMATIC
VALVE
THERMO-PNEUMATIC
VALVES
BLOCK
FAN
CLUTCH
RADIATOR
RADIATOR
FAN
CLUTCH
BLOCK
SHUTTER
BLOCK
BLOCK
THERMO-PNEUMATIC
VALVE
THERMO-PNEUMATIC
VALVE
FAN
OVERRIDE
SWITCH
AIR
CONDITIONING
SIGNAL
AIR COND. COMPRESSOR
SOLENOID VALVES
(NORMALLY OPEN)
FAN
CLUTCH
RADIATOR
CONDENSER
RECEIVER
DRYER
AIR
CONDITIONER
OVERRIDE
SWITCH
FAN
CLUTCH
RADIATOR
SOLENOID VALVE
AIR
CONDITIONING
SIGNAL
AIR
CONDITIONING
OVERRIDE
SWITCH
FAN
OVERRIDE
SWITCH
RECEIVER
DRYER
CONDENSER
AIR COND.
COMPRESSOR
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 thermo-
pneumatic 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
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
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.
SHUTTER
IGNITION
