understanding the ARC

[jcasey007]

Last weekend I replaced among other things the rear shocks, the old ones would sag if load was applied in the boot and the compressor would kick in and pump them up (with the load in the back it would cycle the compressor every 20 seconds.

So after fitting the new back end (i.e. shocks) the ride height is OK but when load is applied and the compressor kicks in the height does not change. again the compressor cycles every 30 seconds (without a change in height and after 30 mins the ARC shuts down and shows as a fault. This is reset following a cycle of the ignition key.

I know the height is not changing as by sitting in the back with a tape measure I can see a deflection of 3cm causes the compressor to kick in and it does not raise up.

So tonight I took the compressor assembly and the solenoid off the car.

I have to assume the new shocks are good! So I'm trying to work out what each of the components do and how the system works.

http://img827.imageshack.us/img827/3711/airtank.jpg

http://img231.imageshack.us/img231/2660/img00193201105081941.jpg

http://img5.imageshack.us/img5/9294/img00194201105081941.jpg


Looking at the compressor assembly, it looks like a standard Piston based compressor with side valves and either an air tank or some posts call it an air dryer. from here the single outlet pipe goes to a solenoid valve and then via a Y piece to both rear shocks.

So how is the flow of air supplied from the compressor and how is air let out of the shocks when they are too high.

I will do some tests on the compressor tomorrow so see if it will pump and I will test the solenoid valve to make sure It opens when power is applied.

does anyone know at what pressure the compressor runs at?

there are 4 wires going to the compressor assembly, 2 go to the motor and the other two go into a box on top of the compressor does any one know what this box does?

all help appreciated

 

[JonC]

I won't speculate on this because others (notably Howard!) will almost certainly know better but while the questions are flying. might I add another relevant to us all?

Is there any kind of intake filter that you can see now it's all in bits (I'm impressed it all came out so well by the way!)?

It's a pretty crap environment it works in and as most of us are running 10-14 year-old motors, we'd be doing them a favour by changing it - if there is one!

Cheers, JC

 

[Stenasev]

So how is the flow of air supplied from the compressor and how is air let out of the shocks when they are too high.

There should be two solenoids that open to supply air. A 'fill' solenoid and a 'balancing' solenoid to control whether air travels between the two shocks or not.

there are 4 wires going to the compressor assembly, 2 go to the motor and the other two go into a box on top of the compressor does any one know what this box does?

This box is the vent solenoid which is how the air is let out to lower the vehicle.

HTH

SS

 

[Howard]

Possibly the default 'level' wants to be reset, as the system has got used to a lower setting. A case of turn it off, jack up the rear so that the axle hangs, lower to the ground and switch it back on.

 

[jcasey007]

Thanks Howard, I did the patented ARC reset procedure, initially the ride height was about 5cm higher but I put this down to springs needing to settle, as soon as I drove it the ride height came straight down to where it was.

Hi Stenasev, I could not see a balancing valve on my truck, the one valve takes a single air feed from the pump and goes straight into a Y piece and then straight off to the shocks. Also there is only one height sensor in the middle of the axle, so I must have a simpler system than yours.

Re the Vent valve, I agree, I guess when it needs to go up the compressor and the downstream valve are both energised, and when it needs to lower the vent valve and downstream valve both get energised. Makes sense.

I'll be able to bench test tonight, If they are ok I might put an airline onto the shocks just to make sure they are not new but defective..... wouldn't be the first time.

cheers

Jim

 

[jcasey007]

I won't speculate on this because others (notably Howard!) will almost certainly know better but while the questions are flying. might I add another relevant to us all?

Is there any kind of intake filter that you can see now it's all in bits (I'm impressed it all came out so well by the way!)?

It's a pretty crap environment it works in and as most of us are running 10-14 year-old motors, we'd be doing them a favour by changing it - if there is one!

Cheers, JC

I don't recall seeing one but to be honest I wasn't looking, I'll check it over tonight.

As it happens the hardest part of getting it out was removing the air lines, I had to cut the ones off the old shocks as rusted but these it is more a matter of technique , a bit of push, push, pull is involved

 

[Stenasev]

Hi Stenasev, I could not see a balancing valve on my truck, the one valve takes a single air feed from the pump and goes straight into a Y piece and then straight off to the shocks.

Hi,

I was only quoting what I had read rather than first hand. The balancing valve must be for true ARC rather than the UK Rear Levelling system. For info, on the (US) vehicles that do have the balancing valve it should be closed to provide assisted stability on cornering and open to provide a softer ride when level. Thinking about it, as you state, the simple height sensor we have would not provide enough info for a balancing solenoid to work.

SS

 

[jcasey007]

looking at the different posts on the US version of the ACR, I'm glad I don't have valves and sensors at each corner on a 14 year old truck

Our system is simpler and as the ride height sensor seems to be detecting correctly it must only be the valve(s) or compressor or connections. I noticed last night that there was a little corrosion on a couple of the plug connections. somthing else to check as well

cheers

jim

 

[jcasey007]

update on testing

OK I managed to do some bench testing this evening, here's what I observed.

Testing the compressor was quite easy, apply power to the plug connections (red and black cables) the compressor runs smooth, free running it draws about 4.5 amps, good supply of air (volume).

I used a good quality foot pump with a pressure guage and connected it to the pump output. I did a static pressure test and achieved 140 PSI which I think should be high enough (no data to support this just gut feel) and it would have gone higher but I wimped out.

Next I tested each of the valves, nice audiable click on both and with my mouth adding a bit of pressure I could feel the valve open on both.

Next I connected the downstream valve to the compressor and built up over 100PSI, applied spit to the valve outlet, no leaks, energised the valve and it opens fine.

Next test again with the downstream valve attached and presurised, I energised the air release valve and yes valve operates as designed to lower the shocks.

I did these tests a few times including a pressure hold test for 10 mins.

So everything looks good on the bench, Tomorrow night I will refit and re-test on the car. Now I know what the unit is designed to do, I can replicate the bench tests in the truck and see what is what

BTW there is no air filter on the intake to the compressor, the best I can figure is the intake comes in from the body of the motor via a plastic tube

jim

 

[jcasey007]

follow up testing

Following on from last nights bench tests....

I fitted the compressor back under the car, wired it back in but didn't connect the pipes.

The suspension is at its lowest point without any air in the shocks and I was able to get underneath safely.

With the ignition on, I was able to manually trigger the system to add air by simply unclipping the control rod from the height sensor, moving the now free arm up, I was able to simulate the suspension being too low.

So all set, first I checked the compressor assembly for operation.- on activation first the air release valve operates, followed about a second later by the compressor - I guess this is to make sure that the comressor does not try to start when there is pressure present in the outlet - I also pressure tested it in the car, ran it up to 130psi - so all good

Next I connected up the downstream valve to the electric and air hose to the compressor, on activation the sequence of operation is - Release valve - Compressor - Downstream valve (about 1 second after the compressor)

All good I thought! with the downstream valve connected (but not to the shocks), the volume and pressure of air is very low, if I connect it to the shocks I get about 5mm of lift and the valve leaks air from somewhere. When I connect the pressure guage to the valve outlet, it barely registers

I figure it is either the downstream valve faulty or a power supply issue to the downstram valve.

So down to Chris tomorrow for a replacement valve and see what's what

cheers

Jim

 

[jcasey007]

Job Done!

turned out it was the faulty valve.

I also need to send an appology to Stansev, my truck did turn out to have two downstream valves, one flowing into the other, A throwback to when it had real ARC.

the system now smoothly goes up and down

Jim

 

[janolsson]

Well done dude. proper diagnostics with a result, great spannering

 

[Howard]

Well done. So now we have an ARC expert on the site.

 

[ihpj]

Cracking thread, sadly I couldn't follow much of the technical aspect of the work completed - except your air suspension wasn't working and now it is (I'm none the wiser why ).

I've disconnected my ARC-shock-thingy (physically unconnected the it from the multi-plug) but left the plastic carrier connected. I found that the lower connection arm was rusted and caused the ARC-shock-thingy and the plastic carrier to hang loose, causing the warning light to illuminate on the dash every now and again.

Given how the system works, I'm quite happy to use my Ex. without it - especially as I wont tow (it doesn't have a tow bar) or put a heavy load that would need it to be 'levelled'.

Hopefully that will be the end of my ARC problems ...