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Another On board air write up


Diff
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Air conditioning compressor converted for ‘On Board Air’:

There are two excellent ‘on board air’ articles in the Tech archive, and I thought I would share details of my slightly simplified system together with relevant info for those contemplating such a useful modification.

I have converted a Sanden SD709 Range Rover air con pump for onboard air.

The newer versions which take the more environmentally friendly refrigerants are numbered SD7H15 and are mechanically and dimensionally the same.

The Sanden air con compressors are commonly found on Range Rovers and Discoverys with both V8 and Tdi engines. They come with either V belt pulleys or serpentine belt pulleys depending on age.

All 2.5 diesel, turbo diesel, tdi and v8 engines have the necessary mounting points on the engine (though some diesels don’t have the four mounting bosses on top of the timing case drilled and tapped). With the right factory bracket, tensioner and bottom crank pulley, fitting is easy.

The Land Rover 4cyl petrol engines don’t have the timing case mountings as standard, so I had to make a bracket for my application. I chose to run mine from a second standard water pump pulley bolted on top of the original.

To keep things simple and cheap, I chose not to buy lots of threaded fittings. I welded a short piece of 13mm steel tube to the compressor’s outlet fitting. This is connected to some ½ inch bore rubber air line with some construction adhesive and a jubilee clip. This rubber air line is connected in the same way to a length of standard 15mm domestic copper tube which runs along the chassis. Towards the end of this copper pipe, I fitted a 15mm domestic water system non return valve. This is then connected to another piece of rubber ½ inch air line to the tank/receiver.

For simplicity, I used the complete tank, switch, pressure relief valve etc from a very small workshop compressor (4 litre tank). The pressure switch was adjustable (although these switches are from 240v compressors, they all work fine with 12volts), so I set it to come on at 90psi and switch off at 130psi. The tank fits neatly on top of the rear wheelbox.

Wiring is very simple. A fused ignition controlled supply goes to the on off/pressure switch on the tank, and from here to the clutch on the compressor in the engine bay.

The York compressor (not commonly fitted to Land Rover vehicles) is sometimes chosen over the Sanden because of the rumours that only the York has a sump for oil lubrication. The Sanden also has a 'sump' in that the wobble plate area under the pistons is also designed to be filled with oil in its original air conditioning application.

Just like the York’s sump, this area is connected to the head by a small passage which is designed to let some of the oil circulate with the refrigerant.

Because of the rotary design of the Sanden as opposed to the ‘crank and conrod’ design of the York, the Sanden design works well for onboard air when the ‘sump’ is filled with grease.

This means that there is no need to fit a coalescing filter to prevent oil getting into the tyres.

The valves in the head of the compressor are simple flaps of stainless steel and require virtually no lubrication. For this reason, I didn’t feel the need to fit an inline oiler to the air intake. A little squirt of wd40 or similar into the intake once in a blue moon is all I do.

The simplest way to get grease into the compressor, is to unscrew the top hex filler plug, and put the nozzle of the grease gun into the hole and pump until full-ish, then replace the plug. It may be that the thixotropic swivel housing grease would be good in this application – I haven’t tried it.

I put a filter on the end of my airline to check that no oil or moisture would get to the tyres. The filter never collects anything. I drain off any moisture from the tank before and after each offroad day, and that seems to be all it needs.

Points to note:

You don’t need an ‘unloader’ type pressure switch for onboard air. Compressor will easily cope with full system pressure in the pipe work etc on startup.

You don’t need a tank for airing up tyres, but it helps to collect any condensation/moisture/oil residue from the air, which is therefore prevented from reaching the tyres, and can be drained off regularly.

I used a 15mm domestic water system non return valve (from Toolstation - £1) because the one fitted to the original compressor tank looked small and restrictive. Conventional air ones are readily available but at higher cost.

Domestic copper tube and fittings are perfectly capable of handling the air pressures.

If you use copper pipe, it should be fitted in a way so that it doesn’t fatigue due to flexing/vibration (use flexible hose at either end).

Use rubber or silicone air hose close to compressor as some plastic types may get soft and weak with the heat. If you wanted to run ARB air difflocks, you can either set the pressure switch to keep the system pressure at the required pressure (will reduce tyre inflation performance a bit), or fit a cheap regulator to the system to feed the ARBs, whilst keeping system pressure high for tyre inflation.

I used a cheap K&N style crankcase filter on the compressor inlet (about £2 new from ebay) I have a large plastic aerosol cap which I fix over the filter which still allows plenty of air flow but stops the filter getting splashed with muddy water.

You can use all sorts of different pressure vessels for the tank, eg fire extinguishers, gas bottles, truck air brake tanks, or whatever. Being able to regularly drain them is important.

A pressure relief valve/safety blow off valve is vital in case the pressure switch fails or the clutch fails to disengage.

I enlarged the compressor head and fitting orifices with a drill (this may not have been necessary) and used as big a bore hoses and pipes as I could, in the belief that it would keep any restrictions to a minimum. Fittings where necessary are ¼ bsp and are the narrowest points in the system. Tool airline is 3/8 inch bore.

Performance:

I only have a tiny 4 litre air tank, but my system will inflate a 32inch tyre from Zero psi to 32psi in only 25 seconds (with the engine at around 2000rpm). It will pump air faster than it can go through the tyre valve, so the compressor will turn itself off and on during filling.

Even with such a small tank the impact gun will undo wheel nuts, as long as they aren't over tightened (cheap impact gun – probably not very efficient).

Useful links:

I discovered reasonable value pressure switches, safety blow off valves etc can be bought from Matt Savage at: http://www.mattsavage.com/acatalog/compressors.html

I have no connection etc.

Sanden specs and workshop manual:

http://www.sanden.com/support/pdf/sd7servicemanual.pdf

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Have fun with your onboard air!

Regards,

Diff

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  • 2 weeks later...

Ok, spurred on by your write-up Diff, I just went out & found a nice shiny SD709 at the local scrappy.

My first problem, since it came from a Clio, is that it has a flat (grooved) belt pulley. Does anyone have a V pulley for a Sanden? Or know if its possible to switch all the other pulleys to Flat?

Cheers

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by any chance do you know if this set-up would work with the Sanden TRS105 compressor as found in the 4.0 and 4.6 V8s?

Hi Chuck, I'm not familiar with that one but assuming it is similar in design to the other Sandens, there is no logical reason why it won't work just as well.

Regards,

Diff

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Ok, spurred on by your write-up Diff, I just went out & found a nice shiny SD709 at the local scrappy.

My first problem, since it came from a Clio, is that it has a flat (grooved) belt pulley. Does anyone have a V pulley for a Sanden? Or know if its possible to switch all the other pulleys to Flat?

Cheers

As far as I know, the multi groove pulley/clutch is interchangeable with the V belt type. Have a look at the Sanden manual I posted a link too, as you may need to fab a puller to get it off easily.

It may be more straightforward to exchange the whole compressor and pulley/clutch with one with the V belt pulley you need. 2.5na and 200tdi need the V belt type, 300tdi need the one you have. Early style V8s will also need the V belt type, though later ones will need the one you have.

Good luck,

Regards,

Diff

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  • 9 months later...

You will definately need silicone Hi temp hose from the compressor :o

On the V8 I mounted mine low down on the l/h side of the engine with a small heatshield due the ex manifold.

The only downside is you get all your mates lining up to have you blow up their tyres as well.

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You will definately need silicone Hi temp hose from the compressor :o

On the V8 I mounted mine low down on the l/h side of the engine with a small heatshield due the ex manifold.

The only downside is you get all your mates lining up to have you blow up their tyres as well.

Hi tacr2man,

Mine has standard 1/2 inch bore rubber airline from the compressor as stated and it is fine. 'Some' Plastic types may go soft or melt if the compressor is worked ver hard. Silicone only required as opposed to rubber if you go near the exhaust as you have found.

Mortus,

Matt Savage has a good selection as stated by TomG. Cheaper alternatives can be found second hand, either from diy compressors whose motors have broken, fire extinguishers, or even a piece of pipe with the ends capped and welded. There are lots of possibilities. As mentioned in my original article, whatever you choose, it is important to be able to drain the condensate off very regularly.

Regards,

Diff

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ive been looking for small tank, can you tell me where to get one?

i was looking at lorry brake tanks. but they seem to big.

I use a co2 fire extinguisher as a tank.

Range Rovers with air suspension have a handy size tank on them.

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G'Day all, new to LR4x4,

but have been playing in the mud for nearly 35 years (damn makes me feel old or should I say wiser)

I've had many variations on this theme and they all come unstuck when you ford deep water and forget that the breather on the compressor has also been immersed. A remote filter near the firewall or better still an outlet on the engine air filter is the way to go.

I had a bad experience with a york compressor and a rangie drowned in a "soupie" mud bath. Whilst running diff' locks the Rangie became a permanent bog fixture, the compressor sucked the brew in and then failed, after much groaning.

You may want to consider a clean air source away from the front of the engine,

Cheers.........Rodd

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  • 3 weeks later...
Hi

Do you have any update on how well the grease does lubricate the pump? :)

Well, I fitted it over a year ago, and it still works perfectly. To be fair it only gets occasional use. Though I have full confidence in the grease. I did a lot of research before going down this route. Some custom car enthusiasts in America who have air powered suspension on their customised pick ups and cars which jack themselves up and down use Sandens filled with grease almost continually with no problems.

SimonR on this forum ran air suspension on his Land Rover continuously for several years with a grease filled Sanden too.

Hope this helps,

Regards,

Diff

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  • 4 months later...

Hi Diff,

I've been researching on how to do this conversion in my Series III 2.5L petrol and your post has given me a bit more confidence. I've not seen anyone add an engine driven compressor in a Series vehicle before so I was hoping to get a little validation that it would work and where to squeeze it in.

Thank you again for such a great post!

Brian

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  • 5 weeks later...

Hi Diff,

Excellent post and after reading it I decided to have a go myself! Only problem I have is my engine is a 300tdi and the only air con pump I can find that seems to fit is made by Denso, this obvioulsy differs from the Sanden by quite a bit and doesn't seem to have anywhere to put grease in to lubricate it. The only thing I can think to do is add an in line oiler to lubricate the pump while it's running but how do I extract the oil on the other side before it reaches the tyres?

I have been giving it a squirt of WD40 for the time being but have been told this will not last for very long!!!!!

Any help as to the best course of action would be much appreciated.

Thanks,

Pete

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I have filled my Sanden one with grease, added a grease nipple instead of the plug AND added an in line oiler! To remove the oil before the tyres I have added a circular flow filter (one with a glass bowl and a tap at the bottom) in the line. Such filters will apparently remove 99.9% of oil and water from the system.

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That sounds exactly like what I need...any idea where I can get one from?

I currently have one of these but have no idea if it removes oil:

http://www.machinemart.co.uk/shop/product/...ipment-air-hose

and it doesn't say on the website.

Unfortunately on the Denso unit there is no plug to put a grease nipple in or non that I can see anyway and without knowing where to drill a hole for a grease nipple it would be risky to write off a perfectly good pump with a mistake.

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  • 4 months later...

Me?

I want to run my aircon to keep me cool but could do with an air supply sometimes. I've been lugging around a compressor but it is starting to go wrong so I am thinking of having an engine powered compressor.

Anyway, it won't work. I've had the engine covers off and there isn't anywhere good to put the second compressor and get drive to it. Might look at a big 12v electric motor linked an air con compressor.

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