MP85.9970
14JUN05
625 TROUBLE SHOOTING GUIDE
GLOSSARY
AIR DUMP - PILOT: The pilot operated air dump system is supplied by the chassis
NOTE: Other types of pilot operated air dump systems may be used such as manually controlled
valves, but the above described system is controlled by the HWH leveling system controls.
AIR DUMP VALVE - HWH: The air dump valve is a normally closed valve that is actuated with
CHECK VALVE - LEVELING SYSTEM HYDRAULIC MANIFOLD: There are two check valves for
CONTROL BOX: The control box utilizes inputs from the touch panel, level sensing unit,
manufacturer. This system uses an electronically controlled two position pilot valve that
switches the suspension from a travel mode to a dump mode. In the travel mode, the height
control valves control the suspension. In the dump mode, the height control valves are isolated
from the air bags and the air is exhausted from the air bags. Only the air in the bags is
exhausted, the air in the rest of the system remains. The pilot valve has a simple 12 volt coil on
each end of the valve. Part of the control harness is supplied by the vehicle manufacturer and
the harness from the HWH control box is supplied by HWH. There are normally three wires in
the HWH harness, a white ground wire, a number 9300 black wire for the dump side and a
number 9301 black wire for the travel side of the pilot valve. The HWH control box switches
+12 volts to control the pilot valve. When power is supplied to either coil on the pilot valve, the
valve remains in that position until power is supplied to the other coil.
a 12 volt coil. When power is supplied to the valve, the valve opens to allow air through. When
power is removed, the valve is closed with a spring. Although there are different arrangements,
the most common is one HWH dump valve for each suspension height control valve. The
dump valve is teed into the air line between the height control valve and the suspension air
bags. When the dump valves are open, they exhaust all the air from the air bags and the
vehicle suspension. Normally the complete harness for this system is supplied by HWH. There
are two wires to each valve, a white wire and a black number 9300 wire. The HWH control box
sw12 volts to open the air dump valves.
each solenoid valve. The check valves allow two solenoid valves to be opened at the same
time without fluid flowing from one jack to the other. This keeps the vehicle from dropping when
one jack is on the ground and another jack is being extended. Although the check valves can be
replaced, HWH should be contacted when there are check valve problems.
manifold and jack pressure switches and jack warning switches to control the leveling
system. The control box supplies outputs to the touch panel to control indicator lights
and to the pump/manifold assembly to control the hydraulic solenoid valves and the
hydraulic pump. The control box also supplies outputs to control the air dump system
if needed. The level sensing unit and the mini blade fuses are the only serviceable parts in
the control box. The control box is mounted to the power unit/manifold assembly. Because
the sensing unit is mounted in the contol box, the orientation of the control box is critical. The
sensing unit may need to be programmed if the control box is replaced.
(SEE LEVEL SENSING UNIT) The ignition must be in the ON or ACC. position and the
park brake must be set for the control box to function. The control box is equipped with
LEDs to indicate different functions are operating. A lit LED indicates a function is working,
JACK CYLINDER: The jack cylinders are hydraulic, single acting cylinders which are used to level and
stabilize the vehicle. The cylinders are extended with fluid supplied by the hydraulic pump under
pressure. The jacks are retracted by the use of a pair of springs which pull the jack up when it’s
solenoid valve is open and the pump is not running. Jack cylinders are mounted to the frame of
the vehicle in a pivot bracket. When a cylinder has a problem such as a leak, only the cylinder
should be replaced. The cylinders are available in different capacities, lengths and spring
arrangements. The capacities are 6,000#, 9,000#, 12,000#, 16,000# and 24,000#.
A
B
B A
LEDs are not turned on to indicate a problem.
