MP85.9971C
03NOV11
625 TROUBLE SHOOTING GUIDE
GLOSSARY
PUMP: The hydraulic pump supplies fluid to extend the jacks and operate any HWH slide
mechanisms. The pump is turned with a +12 volt motor. (Some systems may use a +24 volt
motor) The motor is a replaceable part. The pump motor is internally grounded. This requires
the pump/manifold assembly to have a good frame ground through the mounting of the assembly.
This may require a separate ground cable, minimum size #2, to supply the necessary ground for
the assembly. The oil level in the pump reservoir should be checked with all HWH cylinders,
leveling jacks and/or slides retracted. The oil level should be (1) inch down from the top of the
reservoir fill hole. The pump should not run when the leveling jacks are being retracted. The
pump motor does not have thermal protection built into the motor. The correct pump pressure
should be 3500 p.s.i. When checking the pump pressure, the minimum pressure should be
3300 p.s.i. and the maximum pressure should be 3600 p.s.i. The pump reservoir is equipped
with a breather cap/dipstick that has a 1/4 inch nut driver in the end of the dipstick to manually
open solenoid valves with valve release nuts. The reservoir has to be vented and should never
be plugged tight.
RELAY - MASTER: The master relay is a continuos duty, normally open, four post relay that consists
of one pair of contacts and a coil. The contacts are used to 12 volts to the pump relay
and to the control box. Power in and power out on the contacts can be reversed. The coil is a
+12 coil. There is a small post on the relay for each side of the coil. Either post can be +12 volts
with the other post being ground. The control box sw12 volts to turn the relay on. With
the relay turned on, the contacts will close sup12 volts to the pump relay and the control
box. With the relay off, there should be power on one of the large posts only. With the relay on,
the voltage on both large posts should be the same. With the relay off, both sides of the relay
coil, the small posts, should show a ground. With the relay on, one small post should show +12
volts, the other small post should show ground. If the ground is missing, both small posts will
show +12 volts. The master relay will be on whenever the ignition is on and the park brake is set
or while a room control switch is being pushed to EXTEND or RETRACT with the park brake set.
RELAY - PUMP: The pump relay is an intermittent duty, normally open, four post relay that consists
of one pair of contacts and a coil. The contacts are used to 12 volts to the pump motor.
Power in and power out on the contacts can be reversed. The coil is a +12 coil. There is a small
post on the relay for each side of the coil. Either post can be +12 volts with the other post being
ground. The control box sw12 volts to turn the relay on. With the relay turned on, the
contacts will close sup12 volts to the pump motor. With the relay off, there should be
power on one of the large posts only. With the relay on, the voltage on both large posts should
be the same. With the relay off, both sides of the relay coil, the small posts, should show a
ground. With the relay on, one small post should show +12 volts, the other small post should
show ground. If the ground is missing, both small posts will show +12 volts.
SHUTTLE VALVE: The shuttle valve is located on the leveling system hydraulic manifold. (See
MANIFOLD HYDRAULIC) Fluid flows from the pump to the manifold, through a fitting on top
of the manifold, through a U shaped tube to a fitting on top of the shuttle valve, then into the
manifold to extend the jacks. The fluid flows from the manifold through the shuttle valve back
to the pump when retracting the jacks. The shuttle valve is a hydraulically actuated valve. When
the pump is running, the shuttle valve shifts to allow the the fluid into the manifold. At the same time,
the shuttle valve closes the path for fluid return to the pump. It takes approximately 800 p.s.i. to shift
the shuttle valve. When the pump shuts off, the shuttle valve should shift back to the off position.
This will allow fluid to flow from the manifold to the pump when the jacks are retracted. The shuttle
valve is a replaceable part.
NOTE: There are several different size pump motors used along with a range of different tank capacities.
Also, a few pumps have a relief set at a lower pressure. Due to mounting and operational requirements,
it is important to obtain the proper replacement components or complete unit.
