Sounds like it would be easier to take it out and replace it with a conventional pump

 

Pretty much. The compressor itself is pretty standard and basic so that is basically what I described. You would just need to disconnect it from everything but the tube to the accessory inflator and then figure a way to trigger the relay on the firewall below the brake booster. In reality I think that would actually be easier than replacing it with something else as you already have a working compressor, a place to mount it, power wires already run to it in a nice and safe manner, etc. Might be possible to convert the rear inflator switch to latching or replace it with a latching switch. Then you would have to get wires from that to the relay under the hood which likely are already there in the existing main bundle of wires to the compressor shelf. Would take some time and effort but I think it would be a very elegant solution as it keeps everything basically stock without having to hack much of anything up.

The drawback of course is that H2 are increasing in value and like any vehicle that becomes collectible, originality is huge. Anything taking away from the originality tends to decrease desirability and value. That ship has sailed though (well I guess you could change it back to the air springs)....

 

I can't imagine what the cost would be to change it back.....and the headache

 

Do you understand the difference between the CEL and DIC display?

SERVICE AIR SUSPENSION

If a problem occurs with the suspension system, this
message will appear on the DIC. If this message
appears, stop as soon as possible and turn off the
vehicle. Restart the vehicle and check for the message
on the DIC display. If the message is still displayed,
or appears again when you begin driving, the air
suspension system needs service

 

You will need to know what the sensor resistance is when the truck is stabilized (compressor commanded off) and wire the same value resistor across the ride height sensors. This will trick the module into thinking the system is perfect. I do not believe that there is bias voltage (dummy load) sent out when the vehicle is started. I would like some more info about the codes set to further assist.

 

That still would not work right as the system also monitors the actual amount of air pressure in the bags. While that would probably work to get around the ride height sensors you would also want to make sure to disconnect the ride height button on the dash. If someone were to inadvertently push that the compressor would start running and probably not shut off until a door is opened or the key shut off as it will never see the expected height change in resistance that the sensors will expect. I do know from custom extended my sensor arms to accomodate 2 inch lift blocks under the air springs that the sensors are based on a 5v reference with the "normal" height voltage range being right about 2.4 volts. There is a small bit of a range of acceptable values before the system will kick the compressor on to adjust the height. So yes - could technically even leave the sensors connected (but at least one end removed from the rear trailing arms) and simply figure some way to permanently strap them into a position where they do not cause the compressor to kick on.

But you still would need to figure some way to get around the system monitoring the pressures which will also cause the system to fault. Oceanbrave and I have both really picked the AS system apart over the past couple of years..... One I also wanted to try at one point was to add an air holding tank and have the compressor keep the tank full. When a change is needed, it would be near instant and you could then tap in to add things like an air horn.

 

H2monsta
do you know if doing that actually works?
I always assumed AS ECU would be monitoring the air-pressures in the system.

 

I will look at a schematic and confirm, but every air ride system I know of, and have ever worked on, operates off of ride height sensors. When the sensor levels, it turns the light switch off. The pressure is not always indicative of height and the strategy involved in managing by pressure would be pretty complicated. None- the-less I will verify.

 

H2monsta
To save you looking, there is a 16-Bit microcontroller based AS ECU that controls the complete air suspension system. It resides in a small module on the AS Frame and the whole pcb is weather proofed and sealed in rubber-compound inside a plastic extrusion.

It ECU controls the Compressor Relay, Exhaust Solenoid, the left+right Inlet Valves monitoring the current drawn by each valve for disconnected or short-circuited valves.

It also monitors and controls the following:-

1. Left+Right Ride-Height Sensors, again checking their currents and to ensure they read sensible values.
2. The 5V Reference Voltage which can also be turned On/Off
3. The Pressure Sensor on the Inlet Manifold and so can determine the individual air-bag pressures.
4. The compressor Over-Temperature sensor(s) (twin compressors on the later H2's)
5. The Battery Voltage
6. The Extended Ride-Height Switch and sets the ERH Lamp on the Dash
7. The Tire-Inflator switch and Lamp
8. The on-board EEPROM that stores the Calibrated Ride Height values and also has a check-sum that ties in each ECU so you just can't swap one out without recalibrating.
9. The two-way Serial Comms to the BCM

So yes, it is pretty complicated, more like sophisticated really. In actual fact a lot of the Hummer's electronics is very well designed and made (despite all our troubles)

I mention all this about the AS ECU only because it's very often underestimated, so it's good to have a record here of what it actually does.

Also a Tech2 can monitor many of these values for diagnostic purposes and can calibrate the ride height.

 

This is a complex system. I was a European drivability technician for years and this is more advanced than anything BMW or Mercedes ever put into production. In fact, this system might have been overcomplicated because I know the later GM products did not have as sophisticated of a system. I have done several conversions on newer tahoes/suburbans where we swapped for the conventional strut/spring setup and wired in resistors with no issue.