My wife’s 2008 H2 has started squatting in the rear suspension. Not every day. Usually when it’s cold. Happens 2 or 3 times and then good for a month or so. Usually after starting it pumps back up in about a minute. Anybody else having these issues?

 

Air bags are probably leaking. Common issue after all these years. You can install new bags or swap out for coils.

 

I had the same issue years ago and have it again now. I'm replacing my airbags this weekend. The air bags are rubber and have to be replaced once in awhile like tires do. What is probably happening is that the bags eventually get dry rot at the bottom where they roll up to the cup. The air will slowly leak through the rotted part at the bottom causing the bag to drop until the better rubber folds against the cup and seals it. If it's not remedied soon it could cause your air compressor to overwork itself and shorten it's life. You could convert to coil springs if you want. I'm a fan of the air suspension so I choose to keep it.

 

Both sides dropping equally would be unlucky, the only common thing is the exhaust valve / inlet assembly, but its hard to see a fault that would cause that.

 

Just to add mine does the same thing, it looses about 1/2" per day. As it happens I'm going to change my air-bags soon, when I do I'll post the findings.

 

Well Ive been looking at my old dual AS compressor unit which is a twin system but should be basically the same just beefier.

The dual dual inlet-valve / combined pressure sensor is the key component controlling the air-flow to and from the air-bags. So I dismantled my old one and closely examined it.

No wonder the Hummer has problems, these inlet valves corrode over time, there around 16 O-Rings forming pipe seals and valve seals. ALL mine were contaminated and it's easy to see how small air can leaks can occur.

As I havent found a source of these valves (unless someone knows?) I'm going to clean/service mine, test and keep as a spare.

May even make a video!

 

One day when I finally get caught up with business projects (and that might very well be in 2019 even) I plan on modding my compressor setup pretty heavily.

My plan is to replace a few components while keeping others. I already have most of what I need laying around from old ambulances that we retired from service and scrapped for parts. My plan is to replace the compressor itself with a much beefier one, add in a 5 to 10 gallon air tank, and replace the factory control valves for the rear air with aftermarket valves. The idea is the factory functionality will still work just as it should but to alter the wiring.

The factory has it so that if it detects (or you press the button to raise the rear) that the rear bags need more air it activates the compressor and opens the valves until each sensor is at the desired level. It also does the same to lower the bags just instead it does not activate the pump but instead just opens the dump valves to release air until the desired position is indicated by the sensors.

I'm just going to set it up so that the fill valves are fed from the new air tank instead of directly from the compressor and remove the factory ability to activate the compressor. Instead the new compressor and tank will be activated by a standard pressure switch so that the tank pressure is always maintained as needed. The switch in the rear for filling tires and whatnot will really not be needed anymore as I will replace that tire valve style fitting with a standard air tool style fitting.

In the end this will allow me to use air tools if needed, I'll also install some air horns (have several of those as well from ambulances), and when the factory computer calls for a suspension adjustment the change will be very quick since it will be pulling air from the tank instead of waiting on the smallish compressor to slowly fill things.

In the long run I'd also love to install air bags with an even greater range of motion and give the ability to manually raise or lower the rear by as much maybe 4 inches. Would also love to add that sort of functionality to the front end too but both of these would of course require fully deleting the factory air control setup (which is really not hard to do) and then doing somewhat major suspension modifications which is far more involved to do it right and have it safe and drive well. The rear would actually not be too tough - would need different shocks with a longer range of travel and taller air bags and probably replacing the stock sensors with ones that have a greater range. The front end, that would be getting into some serious and major modifications to make the front adjustable air ride.

 

Having completely reverse engineered the AS Controller all the key functions of the electronics are now known. For example the controller has the ability to measure the current drawn by each valve. At 12V the inlet valves draw 1.4A each whilst the exhaust valve draws 0.6A, these values may be significant.

The controller's key functions are:-

1. Valve current measurement (Inlets & Exhaust as mentioned)
2. Valve controls On/Off (2-off Inlest and Exhaust)
3. Compressor Pressure Measurement (not exposed on TECH2 ?)
4. Compressor Relay Controls On/Off
5. L&R Ride height sensors measurements.
6. Ref Voltage On/Off Control (L&R Ride-Height Sensors
7. Ref Voltage current (probably checks the ride-height sensors)
8. Battery Voltage Measurement
9. Ignition Voltage Detection On/Off
10. Over-Temperature trips 2-off for twin compressor systems.
11. Inflator Switch On/Off
12. Inputs enable i.e. Over-Temp1+2 plus Inflator (not sure why)

Mine has two compressors drawing a total of 12A (6A each) this was probably an attempt to beef-up the compressor.



There is no air-tank as such, just a dryer which oddly has the ability to vent "accumulated" moisture back through the Right Air Intake using a two-way exhaust valve. When Off it connects Air-In to the Compressor, when On it connects Air-In to the Dryer to exhaust (will operate Inlet Valves to vent Air-Bags. This function may be relavent if you add an air-tank.

 

That is very help and interesting. Makes me have to rethink some of the ways I was thinking with adding an air tank. While the controller has all of those functions some of it that is key is whether or not the software is actually monitoring all of them. If it is then some of my ideas would probably trigger error codes on the dash display (service air suspension). Like the valve current measurements and compressor pressure measurements. Easy enough though to just fully disable the factory controller though. There are a number of both mechanical and electronic aftermarket ride height control options available for air ride. On the ambulances I often work on that have air ride those all use a mechanical control for the ride height. It is pretty much a limit switch that you can physically adjust the arm on that electronically either opens a dump valve or a fill valve. Put a giant patient in the back and the bags gets more air... lol. Most also have a manual dump switch to lower the rear for easier patient loading.

 

This is all good information. Rebuilding and modifying the air compressor system is on my short list. I removed my Gobi rack so I could gain clearance in my parking garage and still have an inch or less of clearance. My back end sits high anyway. I'm sure that could be adjusted with a Tech 2. I want to implement a way to lower the height a couple of inches with a switch. It wouldn't be difficult but would surely give me a "Service Air Suspension" message. I have the old single compressor unit and want to install dual compressors. Any recommendations for compressors? I was thinking about 2 Viar 480's or the dual ARB CKMTA12. The ARB puts out 50% more volume. I would also want an air tank or two. A dash light that indicates when the compressor is running wouldn't be a bad idea either. I broke the tab off the leveling sensor arm that holds the rod and the rubber on the rods is rotted so I'm making new stainless rods with heim joints.