HWH 725 Series Leveling — Symptom-Driven Service & Electrical Test Guide

Before you start

Work the checks in order — each step assumes the previous ones passed. Close all manual valve releases first. Reservoir must be full with jacks fully retracted. Suggested tools: 10-gauge jumper wires, a pressure gauge good to at least 3500 psi (HWH specifies a 5000 psi gauge for pump tests), a multimeter, and a 12 V test light. Batteries should rest near 12.7 V and hold voltage under load; grounding problems are a classic root cause, so verify grounds before condemning parts. Never replace the I/O module or touch panel unless a test says so — a wiring fault can damage the new part.

System electrical map

Ignition ACC feeds the red 6120 wire through a 15 A fuse; 6800 (red) powers the touch panel from the I/O module and 6230 (white) is its ground. The master relay (continuous duty, on whenever the ignition is on) feeds the pump relay and module through a 40 A fuse on the #10 wire; wire 8500 is its control. The pump relay (intermittent duty) gets its request on wire 8600 (terminal 6) and feeds the pump motor on terminal 9. Park brake ground arrives on wire 9000 (pin 1 of the 35-pin plug). The master warning light and buzzer share switched ground 7699 through a 5 A fuse. Air-dump systems use 9300 (dump) and 9301 (travel). Touch panel and I/O module talk on a two-wire CAN pair — yellow (CAN high, module pin 22 / MTA pin 1) and green (CAN low, pin 23 / MTA pin 2) — with a 120 Ω terminating resistor at each end: a healthy pair reads 60 Ω ±10% between the two wires. Both link lights flashing means communication is good.

Pump will not run

1. NOT IN PARK/BRAKE lit while pressing a button → park-brake circuit: with the brake set, pin 1 (wire 9000) must show ground.
2. Check the red master- and pump-relay LEDs on the I/O module. Master LED off → check ignition feed, TRAVEL MODE light, link lights, and the 8500 wire for a short to ground (it is about a foot long; make sure its ring terminal is isolated).
3. Master LED on, pump LED off while pressing an UP arrow → terminal checks: +12 V on master relay terminals 1 then 3 (equal, above 12 V); good ring-terminal connections; 40 A fuse; then 8600 from pump-relay terminal 6 (removing and re-touching 8600 while watching the pump identifies a stuck relay vs. module vs. touch panel).
4. Both LEDs on, pump silent → at least 9 V at pump-motor terminal 9 while an UP arrow is pressed means the motor should run (sluggish below 10 V); if voltage is present, replace the pump motor; if not, chase pump-relay terminals 5/6/7 and ground on 8.

A blown 40 A fuse that re-blows usually means a solenoid valve is drawing excessive current: clamp-meter each black valve wire while pressing its DOWN arrow — any valve above 10 A gets replaced.

Pump runs but jacks will not extend (or lift)

Verify fluid, then pump pressure: remove the U-shaped steel tube at the manifold fitting (not the shuttle-valve fitting), install the gauge on the manifold fitting, jump +12 V from pump-relay terminal 5 to 6 to run the pump. Correct pressure is 3500 psi; acceptable is 3300–3600 psi. The relief valve is adjustable (set screw + jam nut on the pump, sometimes on the reverse face) — never adjust it without the gauge attached. Slightly low pressure can be brought up; drastically low pressure with good voltage (10.5 V+ at the motor under load) and a sound relief valve means the pump; good pressure with no movement points at the shuttle valve. One jack that will not extend: watch its solenoid-valve LED (two LEDs should light with any UP arrow). LED on → open the valve manually; if the jack now extends, check for a minimum 8.5 V between the valve's white and black wires — good voltage means the valve is bad. If it still will not extend, gauge that jack's manifold port: pressure but no flow = hose; flow but no movement = jack cylinder; no pressure = solenoid or inner check valve.

Jacks will not retract

The pump does not run to retract; if it does, replace the touch panel. One jack: check its red valve LED, then open the valve manually — if it retracts with the cam open, test for 8.5 V at the valve; if it will not retract even open, suspect the jack return springs, outer check valve, velocity valve (where fitted) or a kinked hose, and last the cylinder. All four stuck: usually the shuttle valve. Field trick: with every jack solenoid valve fully closed (electrically and manually), remove one outer check-valve cap — this lets the shuttle shift so the jacks retract normally with STORE. If a check-valve cap is removed while any jack valve is open the coach drops suddenly and dumps a large volume of oil. All jacks slow: confirm the breather cap is not plugged. Slow/partial single jack: weak return springs or cylinder.

Jack drifts down / will not stay extended

No visible leak: confirm every manual release nut and cam is fully closed. If the valve LED stays on after the button is released, the I/O module is holding it open — replace the module; otherwise replace that solenoid valve. To separate real bleed-down from thermal contraction, extend all four jacks to lift the coach slightly, wait 20 minutes, mark each rod 1 in below the cylinder, and leave the coach undisturbed: cooling oil legitimately moves a rod up to about 3/8–1/2 in. Only valves letting jacks move more than that get changed.

Warning-light and switch tests

Each jack has a normally-closed magnetic warning switch in the cylinder top: retracted, the rod magnet holds the contacts open; extended 1/4–1/2 in they close and ground the light circuit. Red light stuck on with the jack stored → unplug the switch: light dies = switch or rod magnet; stays on = grounded signal wire or module (signal wires share module ground pin 11). No red light with a jack extended → jumper the two pins in the switch plug; light on = bad switch. Harness pins at the 35-pin plug: RF pin 17 wire 2000, LF pin 28 wire 1000, RR pin 6 wire 3000, LR pin 29 wire 4000 (grounds on 6235). Jack pressure switches (stabilize only, never leveling) are normally-open one-wire switches: adjust with the jam nut, 1/4 turn of the body at a time — clockwise if the jack stops short of lifting 1/4–3/4 in, counter-clockwise if it lifts past 3/4 in.

Excess slope circuit

The manifold carries a 50 psi and a 3000 psi pressure switch — do not interchange them. EXCESS SLOPE sets when the pump deadheads at relief and the 3000 psi switch (wire 8100, module pin B8) grounds: jumpering the 8100 pin with the pump running must light the panel in ~2 s and stop the pump. A light with jacks barely loaded means the switch is tripping early — verify with a gauge inline before blaming coach weight.

Level sensing unit

Accuracy tolerance is ±5.4 in front-to-rear and ±1 in side-to-side on a 36 ft coach. The potted unit carries four yellow LEDs underneath that mirror the panel's level lights (opposing LEDs lit = bad unit). Harness: pin 1 blk 0400 rear-low, pin 2 wht 6231 ground, pin 3 red 6121 +12 V, pin 4 blk 0100 left-low, pin 5 blk 0200 front-low, pin 6 blk 0300 right-low; grounding a signal pin must light exactly one panel light. Adjust only screws 1 and 3 (never 2). Unplugging the sensing unit makes the system think it is level — handy for isolating stabilize-mode faults.