Thread: ARB replacement for Wabco SLS compressor

After my second SLS compressor failure due to drowning, I became less keen to simply replace the same pump in same questionable location. The faults were frustrating in that no easy source for (a)piston rings or (b) brush springs were available. Even so, the drenching left all other components in a less than serviceable condition.

Scoring on the composite ring.


Spring failure was the ultimate killer here.


The pump had become so hot the push fit coupling had disconnected letting water and sand in.


This was the starting point for a project to find a replacement better suited to the role and with the option of comfortably acting as an onboard compressed air source for tyre inflation. A previous post to AULRO detailed the ARB CKSA12 installation and, if I recall correctly, the recommendation was to go for the big brother, the CKMA12 if possible.
See: http://www.aulro.com/afvb/discovery-...essor-arb.html
This system is sold as an onboard high volume compressor with cabin switch, loom, relay and pressure switch. The ARB's claimed 50% duty cycle for typical airbag pressures eclipses the puny Wabco at 5%. At a third of the Wabco cost, this thing screams serviceability. The components list and diagram would enable you to build the entire unit from the available spare parts if you wished - this was a good start. Now, a place to mount the device was needed.
After many wheel changes chasing airbag ruptures (yes, I am still an SLS fan!) I became very well versed with the location of the D2 jack. This would have to be the second worst located item on the vehicle - no prizes for guessing my winner. As you can see from the picture, it is a cosy fit in the jack's cubby hole.



I made a mounting plate from 12mm PVC and used a 75mm bolt replacing the existing holder's mounting bolt to fix the plate. I had heard the compressor at a store demo and was a bit concerned with its noise potential, so opted for some rubber mounts in a similar fashion to the Wabco. It's a fiddly assembly job, but the compressor will rotate about its mounting plate and blue heatsink so you can access the mounting nuts and tighten the mounting bolt to the RH guard.


The next move was a bit daring in doing away with the Wabco exhaust solenoid and regulator system which sits on the end of the dryer. Essentially, the mechanism just has to pressure limit and vent airbags to atmosphere when driven by SLABS controller. A 12 volt Festo solenoid valve was used here but some diligent searching should turn up cheaper alternatives. Spade connectors needed here, so the AMP connector gets the snip. The problem however is that the Festo coil has 35 ohm winding resistance and the Wabco is about 16 ohms. This can cause the SLABS controller to detect a fault and stop all SLS activity. Bridge this with a 33 ohm resistor and all is well.



Similarly for compressor drive, the SLS relay in the engine compartment is probably checked by looking at the coil resistance. I thought I could omit the relay and use the ARB supplied relay but no joy. Now the ARB relay looks for a +ve drive and the LR relay is of course -opposite - it is activated by switching to ground. I took a lead from the normally open (#87 I think) terminal to provide +ve drive for the ARB relay and all was well again. The ARB relay is a 40A device and the LR is about 20A so best to use the ARB anyway with peak current to the motor being 24A. Wire in the pressure switch, add some plumbing (1/4" BSP, 6 and 4mm push fit) to complete the SLS bit and away we go.
Only a couple of days testing so far, but observations are: noticeable buzz on pumping (this is reassuring for most SLS drivers I'm sure), audible hiss on exhaust solenoid still under the vehicle (haven't plumbed it to the baffle yet),and best of all - 12 SECONDS FROM STANDARD TO EXTENDED LIFT!
The next phase is to introduce a switching valve and connect it to a quick fit connection on the bulbar for tyre inflation etc… Also should consider water trap and regulator perhaps. (any good sources?)
One wonders why the compressor and valve block weren't located in the engine bay in the first place where it is dryer, cleaner and accessible, but who can spell RRC and EAS?

The heat under the bonnet versus under the car is one consideration.