Operation and maintenance manual

Section 210-0045
Cooling System - Low Temperature Unloader Valve
SM 2152 6-02
2
1. Engine coolant temperature reaches 96°C (205°F).
2. Engine oil temperature reaches 110°C (230°F).
3. Air intake temperature reaches 66°C (151°F).
4. Transmission retarder requested.
When the solenoid valve is de-energised, the flow is
blocked in the pilot line, allowing the relief valve to
operate at its preset 205 bar (2970 lbf/in²), therefore
allowing pressure to be raised at the inlet port (P). This
increase in hydraulic pressure forces more oil through
the engine cooling fan motor, thus increasing the fan
speed.
As soon as the cooling requirement is satisfied, engine
ECU energises the solenoid valve by applying 24V
(refer to Fig. 2). This will result in only minimum flow
being supplied to engine cooling fan motor, therefore
slowing engine cooling fan.
The low temperature unloader valve also has a
integral check valve, that allows oil to pass from the
outlet port (T) to the inlet port (P). This will happen
when the pressure at the output port (T) is higher than
the pressure at the inlet port (P).
FUNCTIONAL CHECK
Numbers in parentheses refer to Fig. 1.
Checking the proper operational function of the low
temperature unloader valve can be simply executed by
removing the electrical harness connection, while
operating the engine at full throttle. An increase in
engine cooling fan speed should be observed.
However, it is advisable to check the pressure setting
of the valve if proper operational function is
questionable. Refer to following procedure for valve
pressure check.
WARNINGS
To prevent personal injury and property
damage, ensure wheel blocks and steering
locking bar is installed prior to executing
functional checks.
Hydraulic fluid pressure will remain
within the system after engine shut down.
Operate the treadle pedal continuously until
the pressure has dissipated before carrying
out any work on the hydraulic system or
serious injury could result.
Follow directly from the checking procedure for the
Priority Unloader Valve. Refer to Section 250-0075,
PRIORITY UNLOADER VALVE.
1. Fit pressure gauge to the diagnostic check point on
the brake manifold valve (port P1).
2. Remove electrical harness connection to solenoid
valve (1). This will render the solenoid valve de-
energised.
3. Increase engine rpm to full throttle (2200 rpm).
4. Take note of the gauge reading. This is the pressure
setting of the low temperature unloader valve, which
should be 205 bar (2970 psi).
5. If pressure setting is too low after following steps 1
through 4:
(a) Ensure engine is operating at full throttle (2200
rpm).
(b) Loosen lock nut on relief valve (2).
(c) Turn setting screw on relief valve (2) clockwise until
correct pressure is observed on gauge.
(d) Re-tighten lock nut.
Note: Always adjust hydraulic pressure on the
increase.
6. If pressure setting is too high after following steps 1
through 4:
(a) Reduce engine rpm to low idle (700 rpm).
(b) Depress foot brake pedal continuously to relieve
pressure in the braking system.
(c) Loosen lock nut on relief valve (2).
(d) Turn setting screw on relief valve (2) counter
clockwise 2 to 3 full turns.
(e) Return engine rpm to full throttle (2200 rpm).
(f) Adjust setting screw on relief valve (2) clockwise
until correct pressure is observed on gauge.
(g) Re-tighten lock nut.
7. Re-connect electrical harness connection to
solenoid valve (1) on completion.
FAULT DIAGNOSIS
Numbers in parentheses refer to Fig. 1.
There are 4 possible points of failure:
1. The solenoid (1) coil, although continuously rated
they may fail after long periods of service. This failure
is protected by the fail-safe design of the valve. If the