On Board Air (OBA)

If you need air to power tools, the garage isn't the only place to call home. A great ption, such as below, is to simply make your own onboard air system. If you have the money, feel free to buy any of the commercially available units.


The first pic is just a general shot from the drivers side.


Jeep on board air system


The second is kind of a bird's eye view from above the compressor- this shot gives a good idea of what everything should look like coming off the compressor. Note that the original fittings were retained. Thes may need to be modified.

On board air


The third pic shows the manifold built out of brass 1/2" pipe thread and street "T's". Note the first one is a regular T, the other three (to the left of the pic) are the straight T's. Also note the 90 degree 1/2" compression fitting to 1/2" pipe thread elbow entering the right side of the manifold.


Jeep OBA


The round black object (below the yellow arrow) with two wires coming off it mounted to the first T of the manifold is the pressure switch from Air Ride Technologies. Kilby uses a similar unit. It is strongly recommend to spend the extra time (not really that expensive) finding one of these smaller switches rather than using one of the bigger, regular air compressor type that you can get almost anywhere.

The next two T's are merely for the front and rear hoses to exit from. Pretty self-explanatory. The third and last T in that picture is a little harder to see, as it is turned somewhat differently from the others. This was to enable the pressure gauge to be read more easily. That gauge was found at Harbor Freight. The end of the manifold is the 150-psi pop off valve. You really must use one of these. If you don't and the pressure switch fails, the compressor could run until either it or any one of many components suffers a catastrophic failure. (bad!) The switch used is for 130-psi. They have one for 150-psi, but it is best to have a margin of 15- 20-psi between the switch's rating and that of the pop off valve. Otherwise, the pop off valve will open up every-time the compressor shuts off.

The last picture shows a close up shot of the filter, the inline oiler, and the unloader/ one way valve. The unloader valve unloads the pressure from the compressor side of the manifold after it shuts off- this is so it does not have to start up against a load. The one-way valve does just what it sounds like- it only allows air to travel in one direction- from the compressor to the manifold, in this case. It really is a pretty simple thing to do.

Two more recommendations:

First: Do not use Teflon Tape- instead, go to your parts store and purchase a bottle (can?) of liquid Teflon (it is applied with a small brush that is built into the cap.

Second: Be very careful when installing any reducer bushings, so that you do not deform them. I put the reducer bushing for the pop off valve in the manifold before I had put the valve in it, and due to the soft properties of the brass, I partially smashed it. Even though I did my best to fix it, and used extra Teflon, it still leaks. The result is that all my air leaks out a few minutes after I shut it off.


Power your air tools on the trail


The wiring goes as follows:

Fused 12 volts enters the cab, and goes to a toggle switch. From there, it goes back out to the pressure switch (PS), out of the PS to a relay, and from the relay to the compressor clutch. You will notice that there are 2 wires at the clutch. Use both of them. I simply crimped both of them in the same connector.

The oiler works as follows:

You fill it with air tool oil, and as you imagined, there is a tiny orifice (hole) that it is drawn through as air flows through the inlet side. It seems to work ok, but the oiler I have (it was free) is quite difficult to fill without making a huge mess, so I have been simply lightly soaking the filter itself (on the top side only) with the air tool oil, and allowing it to be drawn from there. No more often it runs, and the duration being as short (relative to it's designed use as an AC compressor that runs nearly continuous) as it is. I think either or both methods would be sufficient. I currently have no plans to add a separator. I hooked a blow-gun to the hose and blew it through a piece of cloth (shop rag), and the amount of oil/ moisture that collected on the rag was negligible. If you were planning to run air tools, or perhaps an ARB, you may need to add a separator.

The relay is pretty simple. There are instructions on the packages of most of the ones I have ever bought. It gets fused 12 volt + power (25 amp), chassis ground, switched power (more on this later) and output power. Switched power is 12 volts+ coming from a switch (toggle, for example). I ran a 5 amp fused power wire into the cabin, and into a toggle switch. From the toggle, I ran a wire out to the engine compartment to one side of the pressure switch (PS). From the other side of the PS I ran a wire to the switched power terminal of the relay. So basically, when I need air, I turn it on at the toggle switch. The PS determines whether there is a need for the compressor to run (mine comes on below 115-psi, and shuts off at 130-psi). If it is below 115-psi, it connects and sends 12 volts to the switched power post of the relay. This triggers the heavy duty switching terminals inside the relay, and sends power to the compressor clutch, engaging it. Ta-Da! We have air.

One thing that I am going to change, is the copper tubing that runs from the compressor outlet to the air "manifold" at the passenger side fender. I do not have the manifold securely mounted at this point due to the fact that it is more or less stiffly connected to the comp. As you know, the engine can twist in place slightly, and the fender does not. If I were to mount the manifold to the fender, the copper tubing could either be pulled apart from it's fittings, or fatigue over time and rupture. I am going to replace a portion of it with 3/8 or 1/2" air hose, and mount the manifold.