MP85.9971A
03NOV11
725 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
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 I/O module 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 I/O module 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 I/O module
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.
JACK CYLINDER - STRAIGHT-ACTING (PIVOTING JACK) W/SPRING RETRACT:
A
B
B A
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. The jack cylinder can pivot inboard and outboard slightly when mounted into the
jack pivot bracket. The foot of the jack also pivots. The foot is attached to the cylinder with a
nut. 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 4,000#, 6,000#, 9,000#, 12,000#, 16,000# and 24,000#.
JACK - STRAIGHT-ACTING (FIXED MOUNTING) W/SPRING RETRACT:
is a hydraulic , single-acting cylinder that mounts directly to the frame of the vehicle. The jack
cylinder has no pivoting action but the foot does pivot. The foot is attached to the cylinder with
a nut. The jack is extended with hydraulic pressure and is retracted with a pair of springs. The
Straight Acting jack with a fixed mounting should eventually be available in a full range of
capacities 4,000# thru 24,000#.
The straight-acting jack
