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Air Suspension and HWH Explained

 

1. PREFACE

In “Introduction to Air Suspensions” in our online technical school, the discussion was about what an air suspension is, how it works and some of the basic components of the air suspension. If you have not reviewed that section yet, it would be helpful to do so before continuing with this discussion. If you are confident you understand air suspensions, especially height control valves and pressure protection valves, please continue.

This section will deal with how the HWH hydraulic leveling systems interface with the air suspension. We will discuss several types of suspension air dumps. We will also discuss how the HWH air leveling systems interface with the air suspension to level the vehicle with the suspension air bags.

2. HYDRAULIC LEVELING AND AIR SUSPENSIONS

2-1 How air suspensions affect hydraulic leveling. Several factors combine to create issues when a vehicle with an air suspension is being leveled with a hydraulic leveling system. The two main factors are the compressibility of air and the transfer of weight through the suspension. As jacks lift a side or end of the vehicle, the suspension will usually shift weight to the other side or end of the vehicle. The added weight compresses the air in the suspension air bags causing that side of the vehicle to lower. This brings the suspension height control valves into play. They start to raise the side that is being forced down with added weight. This can defeat the action of the leveling jacks.

In other words, the air suspension fights the leveling system. As the jacks are trying to turn out the leveling lights, the air suspension in moving the opposite side or end, causing the leveling lights to possible stay on longer than they should. The two sides most likely will seem to lift back and forth making the vehicle level at a much higher level than it should, if it can even achieve a level position.

More than likely, this will create a bigger problem with side to side leveling, because of the much shorter distance, than front to rear leveling. This problem is easily conquered. All you have to do is take the suspension air bags and height control valves out of the equation.

This is done by exhausting all of the air from the suspension air bags and disabling the height control valves. There is several ways to accomplish this. One way uses a normally closed set of valves supplied by HWH to dump the air from not only the air bags but also from the main air supply. The other way uses a pilot valve arrangement supplied by the chassis manufacturer to exhaust air from the air bags and isolate the height control valves from the air bags. We will discuss each method individually.

2-2 HWH air dump system. The HWH air dump system uses normally closed solenoid valves to dump the air from the vehicle suspension. The valves are teed into the air line that goes from the height control valves to the air bags. Usually there will be one air dump valve for each height control valve. Depending on the suspension arrangement, sometimes it is possible to get by with two dump valves; one for the front suspension air bags and one for the rear suspension air bags. If installing a hydraulic leveling system on a vehicle with an air suspension, always contact HWH to obtain the proper air dump kit. The dump valves are controlled by the HWH leveling system controls. This type of system can be used with an automatic leveling system or a manually controlled leveling system; either touch panel or lever controlled.

The following is a basic plumbing diagram for an HWH air dump system.

HWH Suspension

 

Again, note that the HWH air dump valves are plumbed into the system between the height control valves and the suspension air bags. Also note that on this drawing I have included the vehicle air supply along with the pressure protection valve. Remember, as the vehicle lowers, the height control valve linkage opens the valve to allow air to flow from the vehicle air supply into the air bags. This does happen as the air is dumped from the air bags and the vehicle lowers. When the HWH air dump valves are opened, they not only dump air from the air bags but also (through the height control valves) from the vehicle air supply. One of the important rules to follow when using an HWH air dump system is the vehicle engine must be off. If the vehicle engine is allow to run while dumping air and leveling the vehicle, the vehicle air supply will not dump properly. The vehicle engine air compressor will continue to fill the vehicle air supply. When the HWH air dump valves are closed, air from the vehicle air supply will be allowed to flow to the air bags if a height control valve is still in a down position after the leveling process is complete. If the system performs properly, at least one height control valve will probably be in the down position. Now the air bag for that height control valve will lift the vehicle back towards ride height. One or more jacks will not be on the ground. It will appear a jack has not extended properly or it retracted when it shouldn’t.

2-2.1 Valve information. The HWH valve is a simple, normally closed, electrically operated solenoid valve. The coil of the valve is a two wire potted coil that is reversible. That means the coil should be water tight and the polarity of the coil wires does not matter, as long as one wire is + voltage and the other wire is ground. The + voltage side of the coil will always be the switched (control) side. The ground should be constant. The coil of the valve is a continuous duty coil and should open with 8 volts at the coil. The valve ports are labeled “1” and “2”. We use port 2 for the inlet air pressure and port 1 is the outlet or dump side. Port 2 puts air pressure on the top side of the valve seat; this helps keep the valve closed.

HWH Suspension

 

2-2.2 Air dump operation. Except for the older 4 lever systems, the 400 series paddle switch systems and 210/225 joystick systems, all HWH control panels will have a rocker switch or pushbutton for manual air dump control. The 210/225 systems have a harness that furnishes a wire for a rocker or toggle switch. A harness for the air dump valve connections is also supplied. HWH supplies a momentary toggle switch with a small air dump label. The installer can supply a different switch. It is recommended that this switch is a momentary switch with a continuous capability of 10 amps.

For most systems, to use the manual air dump button, the ignition must be on, the park brake must be set and the control panel must be on. For the 625 single touch systems, the manual dump button will work with only the ignition on and park brake set. For all systems, the manual dump button is a momentary button and will have to be held on while dumping the air. When the button is pushed, the + voltage is turned on. The valve coil is energized and the valve seat is opened. The air will now be dumped from the air suspension. When the button is released, the + voltage is turned off and the valve seat closes. The air will stop dumping. With the air dump valves closed, the height control valves can cause the air bags to inflate, raising the vehicle back to ride height provided there is sufficient air pressure in the air supply.

As stated earlier, the air must be dumped from the vehicle suspension before the leveling procedure is started. For manual systems and automatic systems being operated manually, the dump button must be held until all air has exhausted from the air bags and suspension system. This means holding the dump button until you do not hear any more air escaping from the valves. You can also use the air pressure gauges to see when no more air is escaping. When the air pressure gauges stop moving, that should indicate leveling can begin.

Automatic systems will energize the air dump valves automatically before the leveling procedure is started. It is not necessary to manually dump the air. Systems with kick down style jacks will start the air dump when the on (HYD) button is pushed a third time. Non-single step systems will start the air dump when the on (HYD) button is pushed the second time. Single step systems will start dumping air as soon as the LEVEL button is pushed. Air will dump from the suspension for approximately 20 seconds before the leveling process is started. The leveling process starts automatically after the 20 second delay. The system will keep the air dump valves energized throughout the leveling process and turn the valves off after the leveling process is completed and the system shuts off.

It is important to understand the pressure protection valve on the vehicle air supply. This valve maintains a specific amount of air pressure in the vehicle air supply for the vehicle air brake system in case of a problem with the vehicle air suspension system or other non-brake related air equipment. This is why after no more air is exhausting from the suspension air dump valves the vehicle air system pressure gauges will still show 65 to 70 psi air pressure in the system. All RV related vehicles that I have encountered have either two pressure gauges or one gauge with two needles. Depending on how the vehicle air tanks are plumbed into the system, both gauges or needles will drop to the 70 psi range or possibly just one gauge or needle will drop. In either case, when no more air is exhausting from the air dump valves, there should be approximately 65 or 70 psi remaining in the vehicle air system. This can create a problem for the leveling system.

The pressure protection valves are not required to be a “zero” leak valve. This may allow air to leak by the protection valve to the vehicle suspension. Over a period of time, depending on the size of the leak, height control valves in the down position will allow this air to flow to its air bag. This can lift the vehicle, raising one or more jacks off the ground. This can make it appear these jacks are retracting by themselves.

To check this, simply turn the leveling system controls on and push the manual “DUMP” button. If air starts to exhaust from the air dump valves, and the vehicle lowers, the protection valve is leaking. The problem is that because the protection valve is not a zero leak valve, there is no real repair for this unless the leak exceeds the allowable DOT tests. Even putting a new protection valve in the system will not guarantee a solution for the problem. Pumping the brake pedal to lower the air pressure in the vehicle air supply to approximately 30 psi is the only real solution. As long as there is not enough air pressure to actually raise the vehicle, a leaky protection valve will not affect the system.

Returning a vehicle to ride height is very simple; start the engine and build up some air pressure. The air dump valves should be closed unless the system is in an automatic leveling mode or the control panel is on and the dump button is being pushed. As the vehicle lowers when the jacks are retracted, the height control valves will be in the raise position. Air will be directed to the air bags until the vehicle is at the correct ride height.

WARNING: DO NOT CRAWL UNDER A VEHICLE UNLESS THE FRAME OF THE VEHICLE IS PROPERLY SUPPORTED. DO NOT USE THE AIR SUSPENSION OR LEVELING JACKS TO SUPPORT THE VEHICLE WHILE UNDER THE VEHICLE.

2-2.3 HWH air dump valve diagnostics. The diagnostics for the air dump valves is also very simple.

If the valves will not dump air, first determine if one or all valves will not dump air. If no valves will dump air, the control box or panel would probably be the best place to start. If any one valve is working, that indicates the control box or panel is working. (The 4 lever 100/110 systems have two separate outputs for the front and rear valves. Although unlikely, if front or rear valves are working and the others are not, it could be the control panel.) In either case, starting at the dump valves should always get you to the problem. First, check the exhaust ports of the valves for blockage; these ports can become clogged with dirt or small bug homes. If the ports are not plugged, check for voltage between the two wires for the valve. You need at least 9 volts (with the valve plugged in and turned on) to open a dump valve. If good voltage is present, the dump valve is bad. If voltage is not present, work your way back to the control box or panel to determine where the problem lies.

If the vehicle will not return to ride height, check to see if air is exhausting from the dump valves. If no air is exhausting from the dump valves, the problem is with the vehicle suspension, probably the height control valves. If air is exhausting from a dump valve, unplug the valve. If the valve continues to exhaust air, the valve is the problem. If the valve closes when unplugged, the harness wires are shorted to + voltage or the controls are bad.

2-3 Pilot air dump systems. The valves and other equipment for a pilot air dump system are provided by the vehicle or chassis manufacturer. This type of system can be controlled mechanically or electrically. Electric controls can be provided by the vehicle manufacturer or can be part of the HWH leveling system.

The diagram represents a typical pilot air dump system. It is important to understand that this equipment IS NOT supplied by HWH. This equipment is supplied and installed by the vehicle or chassis manufacturer. It is important for you to contact the manufacturer before diagnosing or attempting to repair a pilot air dump system. For a detailed review and explanation of the pilot air dump equipment, refer to the vehicle or chassis manufacturer.

HWH Suspension

An advantage of using a pilot dump system is that the dump valve isolates the air bag from the height control valve while dumping the air from the air bags. Air is not dumped from the main air supply and the vehicle engine can be run during a leveling procedure. Another advantage is the pilot dump valve stays in the position it is shifted to. This means there should be no problem with air seeping into the air bags after the leveling procedure is finished. BUT, this can also be a disadvantage if there is a system failure. If a failure causes the pilot valve to not shift into the travel position, the vehicle cannot return to ride height.

2-3.1 Pilot air dump equipment. The pilot air dump system consists of a pilot control valve and a dump valve at each height control valve along with the necessary plumbing and wiring. The electrically operated pilot control valve has an electric coil on each side of the valve. Switched + voltage is used to energize these coils. When a coil is energized, the pilot valve is shifted to the travel or dump position. In the travel position, the pilot control valve connects the individual dump valves to an exhaust port. This allows the dump valves to shift to the travel position, allowing the height control valves to control the air in the air bags. In the dump position, the pilot control valves uses air pressure to shift the individual dump valves to the dump position. In the dump position, the height control valves are isolated from the air bags and the air is exhausted from the air bags.

Note: Air pressure is required to shift the pilot control valve from one position to another. If the system air pressure is low, the valve may not shift until adequate air pressure is built up in the system with the engine air compressor.

HWH Suspension

2-3.2 HWH pilot dump controls are part of the system control box or control panel. There will be a + voltage output for dump and travel. With a touch panel controlled system, each output will be fused. With a 200 series joystick leveling system, both outputs are protected with the main panel fuse. HWH supplies a harness to connect to the pilot control valve. This harness has three wires in it and terminates into a 4 pin UML connector. The three wires are a black wire labeled 9300 for the dump signal, a black wire labeled 9301 for the travel signal and a white wire for ground. One end pin has no wire, the next wire is the white ground wire, the next wire is the black 9301 travel wire and the other end pin is the black 9300 dump wire. Refer to system electrical connection diagrams for specific control box or panel connections, fuse locations and led information where applicable.

2-3.3 Pilot dump operation. Each different type of control system operates the pilot dump system a little differently. One thing that is consistent between all of the systems is that the ignition must be on and the park brake must be set for the pilot dump system to dump the air. Another consistent feature is when the ignition is on and the park brake is off, there is a + voltage signal to the travel side of the pilot control valve.

There are several types of pilot dump controls for past or present, manual and automatic systems.

1.) There is a rocker switch panel that can be used with or without any leveling system. The panel only has a fuse and a rocker switch. With the ignition on and the park brake set, push the rocker to “AIR DUMP”. This will shift the pilot control valve to the dump position and the air will dump from the air bags. With the ignition on, push the rocker switch to “TRAVEL”. This will shift the pilot control valve to the travel position. The air bags should start to fill and the vehicle should return to ride height. If the ignition is on and the park brake is released, the pilot control valve will shift to the travel position.

HWH Suspension

2.) The light panels for the 200 series joystick systems can operate pilot air dump systems. There are two different 200 series panels. (Shown on previous page.) One has a “DUMP” button and one does not. Winnebago used the panel without the “DUMP” button. With either panel, the ignition must be on and the park brake must be set to dump the air. The panel without a “DUMP” button will shift the pilot control valve to the dump position when the “ON” button is pushed. The signal to the pilot control valve is constant until the “OFF” button is pushed or the ignition is turned off. On the panel with the “DUMP” button, the “DUMP” button must be pushed to shift the pilot control valve. The “DUMP” button is momentary but the signal to the pilot control valve will be constant after the “DUMP” button is released. These panels have a button with a symbol that looks like a rabbit. This is the travel button. With the ignition on, push the rabbit button. The pilot control valve will shift to the travel position. The air bags should start to fill and the vehicle should start to return to ride height. The travel signal will be constant after the rabbit button is pushed and released. If the ignition is on and the park brake is released, the pilot control valve will be shifted to the travel position. The travel signal is constant with the park brake off and the ignition on.

HWH Suspension

3.) 310 series touch panel systems have two different panels, with and without a “DUMP” button. The panel without a “DUMP” button was mainly used by Winnebago. This panel would send a +12 volt signal to shift the pilot dump control valve to the dump position when the “ON” (I) button was pushed. The ignition switch must be in the “ON” position and the park brake must be set for the system to send a dump signal. The dump signal is present only while the “ON” button is being pushed. The panel with a “DUMP” button must have the ignition on, the park brake set and the panel must be on for the “DUMP” button to work. When the “DUMP” button is pushed, the panel will send a +12 signal to shift the pilot dump control valve to the dump position. The +12 signal is only present while the “DUMP” button is being pushed. Both panels have a button with a symbol that looks like a rabbit. This is the travel button. This button works with the panel off or on, the park brake set or off but the ignition must be on. The travel signal is a +12 signal and is only on while the travel button is being pushed. If the ignition is on and the park brake is off, the travel signal will be constant.

4.) 305/325 short board touch panel systems all use the same touch panel; systems with pilot air dump, HWH air dump valves or no air dump. No 305/325 panels have a “DUMP” button. The ignition must be on (or in accessory) and the park brake must be set to dump air. When the “LEVEL” (I) button is pushed, the panel sends a ground signal to the control box. The dump relay is turned on and a +12 signal is sent to shift the pilot dump control valve to the dump position. The signal is constant until the “OFF” button is pushed or the ignition is turned off. The ignition must be on to shift the pilot control valve to the travel position. The panel must be off. Pushing “STORE” signals the control box to send a +12 signal to the pilot control valve to shift to the travel position. The signal is constant. If the ignition is on and the park brake is off, there is a constant +12 travel signal to the pilot control valve.

HWH Suspension

5.) 325 long board touch panel system. This is a manual touch panel system. The touch panel has a “DUMP” button and is the same panel for either the pilot dump system or the HWH dump valve system. The ignition must be on (or in accessory), the park brake must be set and the touch panel must be on for the “DUMP” button to work. When the “DUMP” button is pushed, the control box turns the travel relay and the dump relay on. The travel relay is a normally closed relay so when the dump button is pushed, the travel relay contacts open and the dump relay contacts close. This supplies a + voltage signal to the pilot control valve to shift the valve to the dump position. The signal is constant until the “OFF” button is pushed or the ignition is turned off. After the “DUMP” button has been pushed, any time the ignition is turned on, the control box will pulse the dump relay on to make sure the pilot control valve stays in the dump position.

To return the pilot control valve to the travel position, the ignition must be on. If the park brake is on, pushing the “STORE” button will turn off the travel relay. When the travel relay is off, the normally closed contacts of the travel relay direct + voltage to the pilot control valve. The pilot valve shifts to the travel position. The travel signal is then constant any time the ignition is on. If the ignition is on and the park brake is released, the travel relay is turned off and a constant + voltage signal is directed to the pilot control valve.

HWH Suspension

6.) 610 central ground automatic leveling system. The ignition switch must be on, the park brake must be set and the touch panel must be on to shift the pilot control valve to the dump position. Pushing the “DUMP” button sends a + voltage signal to the pilot control valve. This shifts the valve to the dump position. The dump signal will only be present when the “DUMP” button is being pushed. Also in the automatic mode, the leveling system sends a + voltage dump signal to the pilot control valve. When the “ON” (HYD) button is pushed to start the actual leveling process, a + voltage dump signal is sent to the pilot control valve to shift the valve to the dump position. There is a delay of approximately 20 seconds after the dump signal is sent before the leveling process is started. The dump signal is constant until the automatic leveling process is finished and the touch panel shuts off. The ignition must be on to shift the pilot control valve to the travel position. If the park brake is set, the “STORE” button must be used to shift the pilot valve to the travel position. The touch panel must be on. The travel signal will be constant while the STORE indicator light is on. Any time the ignition is on and the park brake is released, there will be a constant + voltage travel signal to the pilot control valve.

7.) 625 automatic leveling system. The touch panel has a “DUMP” button and is the same panel for either the pilot dump system or the HWH dump valve system. The ignition must be on (or in accessory), the park brake must be set and the touch panel must be on for the “DUMP” button to work. When the “DUMP” button is pushed, the control box turns the travel relay and the dump relay on. The travel relay is a normally closed relay so when the dump button is pushed, the travel relay contacts open and the dump relay contacts close. This supplies a + voltage signal to the pilot control valve to shift the valve to the dump position. The signal is constant until the “OFF” button is pushed or the ignition is turned off.

For automatic leveling, when the “ON” (HYD) button is pushed to start the actual leveling process, the travel relay and the dump relay is turned on. This supplies a + voltage signal to the pilot control valve to shift it into the dump position. The dump signal is constant until the touch panel turns off or the ignition is turned off. After the “DUMP” button has been pushed or the automatic leveling function is used, any time the ignition is turned on, the control box will pulse the dump relay on to make sure the pilot control valve stays in the dump position. To return the pilot control valve to the travel position, the ignition must be on. If the park brake is on, pushing the “STORE” button will turn off the travel relay. When the travel relay is off, the normally closed contacts of the travel relay direct + voltage to the pilot control valve. The pilot valve shifts to the travel position. The travel signal is then constant any time the ignition is on. If the ignition is on and the park brake is released, the travel relay is turned off and a constant + voltage signal is directed to the pilot control valve.

8.) 625S single step automatic leveling system. The touch panel has a “DUMP” button and is the same panel for either the pilot dump system or the HWH dump valve system. The ignition must be on (or in accessory) and the park brake must be set for the “DUMP” button to work. When the “DUMP” button is pushed, the control box turns the travel relay and the dump relay on. The travel relay is a normally closed relay so when the dump button is pushed, the travel relay contacts open and the dump relay contacts close. This supplies a + voltage signal to the pilot control valve to shift the valve to the dump position. The signal is constant until the “EMERGENCY STOP/CANCEL” button is pushed or the ignition is turned off.

For automatic leveling, when the “LEVEL” button is pushed to start the actual leveling process, the travel relay and the dump relay is turned on. This supplies a + voltage signal to the pilot control valve to shift it into the dump position. The dump signal is constant until the leveling and stabilizing process is complete or the ignition is turned off. After the “DUMP” button has been pushed or the automatic leveling function is used, any time the ignition is turned on, the control box will pulse the dump relay on to make sure the pilot control valve stays in the dump position. To return the pilot control valve to the travel position, the ignition must be on. If the park brake is on, pushing the “STORE” button will turn off the travel relay. When the travel relay is off, the normally closed contacts of the travel relay direct + voltage to the pilot control valve. The pilot valve shifts to the travel position. The travel signal is then constant any time the ignition is on. If the ignition is on and the park brake is released, the travel relay is turned off and a constant + voltage signal is directed to the pilot control valve.

2-3.4 PILOT DUMP DIAGNOSTICS. For HWH, pilot dump diagnostics consists of testing for a + voltage signal to shift the pilot control valve to the dump or travel position. All HWH systems that control the pilot dump have a straight 4-pin UML connector with three wires that connect to a harness supplied by the vehicle manufacturer. There are two black wires (9300 – Dump & 9301 – Travel) and one white wire for ground. The hardest part of diagnosing a pilot dump issue will be determining which HWH system is being used and where to locate the 4-pin plug. Contact HWH Corporation for assistance with either issue. Refer to the above information to determine when there will be a signal for dump and travel.

Check the appropriate fuse. If the fuse is ok, then check for + voltage between the appropriate black wire (9300 – Dump & 9301 – Travel) and the white ground wire. If voltage is present, the issue is with the pilot dump equipment and you should contact the vehicle or chassis manufacturer. If voltage is not present, check for voltage on the correct output pin. If voltage is present, there is a problem with the harness wires or connections. If voltage is not present, the problem is most likely the control box or panel. If the fuse is blown, unplug the 4-pin UML connector and replace the fuse. If the fuse now blows, there is a short in the harness or control box/panel. If the fuse does not blow with the harness unplugged, the problem is with the vehicle pilot dump wiring or equipment. Contact the vehicle or chassis manufacturer.

HWH Suspension

HWH Air Leveling System Explained

© Barry Brideau 2003-2017