Chrysler RAM TRUCK 2500 1994 Service Manual page 919

13 - 6 BUMPERS AND FRAME
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SOLENOID VALWE A
The solenoid valve A cartridge contains a poppet
valve. This valve is normally de-energized i n the
CLOSED position. When closed, the valve retains
pressure i n the lift cylinder. When i t is energized
(valve opened), i t allows the fluid to flow from the lift
cylinder back to the reservoir. This enables the plow
blade to lower via gravity.
Solenoid valve A is designed to remain energized
(valve open) during plowing to provide a floating
blade position. This ensures that the plow blade is
guided up-down by the surface deviations.
SOLENOID VALVE B
The solenoid valve B cartridge contains a spool
valve. This valve is normally in the de-energized
CLOSED position. This allows the fluid to flow to the
C solenoid. I n the energized OPEN position, the fluid
is diverted to the lift cylinder. This causes the plow
blade to be raised.
SOLENOID VALVE C
The solenoid valve C cartridge contains a spool
valve that is normally in the de-energized CLOSED
position. This allows the fluid to flow to the right-
side power angling cylinder. This angles the blade to
the left. A t the same time, i t allows the fluid from
the retracting left-side power angling cylinder to re­
turn to the pump reservoir.
Energizing the solenoid valve will route fluid to the
left side angling cylinder. This angles the plow blade
to the right. Also, the fluid is forced from the retract­
ing right side cylinder. I t flows through the C car­
tridge valve and returns to the pump reservoir.
MECHANICAL HYDRAULIC VALVES
The mechanical hydraulic valves all have the same
function: they control the direction of the hydraulic
fluid flow.
CHECK VALVES
Check valves allow fluid to flow freely i n one direc­
tion while preventing fluid from flowing i n the oppo­
site direction.
A pump check valve is used to prevent fluid from
leaking back through the pump to the reservoir.
Two additional check valves are necessary because
solenoid valves B and C have some leakage.
One check valve is located between solenoid valve
B and the lift cylinder. I t prevents fluid i n the lift
cylinder from leaking back through solenoid valve B.
I f fluid leaks back, i t could angle the blade to the
left. This would force fluid through solenoid valve C
into the right side cylinder.
The other check valve is located between valve B
and valve C. I t prevents fluid from being forced
through solenoid valve B.
PILOT CHECK VALVE
A pilot check valve has a piston i n addition to a
ball seat and spring. A pilot check valve is located be­
tween solenoid valve C and the reservoir. I t has two
functions:
• Prevents the hydraulic fluid in either angling cyl­
inder from leaking back to the reservoir.
• Allows the hydraulic fluid from a retracting an­
gling cylinder to return to the reservoir.
The valve action is done by fluid moving the piston,
which forces the check ball off its seat.
CROSSOVER RELIEF VALVE
This valve protects against damage by a sudden
impact against the end of the blade. This will cause
high hydraulic pressure to accumulate i n one of the
angling cylinders.
The hydraulic pressure increases enough to open
the crossover relief valve. The valve allows the highly
pressurized hydraulic fluid to flow to the other cylin­
der. This cushions the impact and changes the posi­
tion of the blade.
SYSTEM OPERATION
Refer to Figures 2 through 5 for voltage application
and hydraulic fluid flow for each snow plow function.
Each figure shows the components that are actuated
for each function.
SNOW PLOW WIRING DIAGRAMS
Refer to Figures 6, 7 and 8 for wiring diagrams.
Refer to Specifications chart at the end of this
group.
SNOW PLOW MALFUNCTION DIAGNOSIS AND
TESTS
Refer to the charts and illustrations for proper di­
agnosis.
SOLENOID VALVE COIL FUNCTIONAL
T E S T
Test the coils for proper operation, according to the
following procedure.
(1) Hold a screwdriver blade about 0.125 inch
above the nut on the coil to be tested.
(2) Have a helper operate the control switch that
energizes the applicable coil.
CAUTION: Do not connect an ohmmeter to a coil
when it is applied. This c a n c a u s e internal damage
to the ohmmeter.
(3) I f the coil is working, the electromagnetic ac­
tion will pull the screwdriver down to the retaining
nut. I f this does not occur, use an ohmmeter to check
the coil for continuity.