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Fast On Board Air

4.3LXJ

NAXJA Forum User
Location
Chico, CA
I had a couple of requests for specifics on setting up on board air, or OBA in short hand terminology. There are thee types. One is the C02 or N2 tank that you have filled to a very high pressure and run a regulator off it to lower the pressure to fill tires etc. The second is the electric compressor kit such as what Viair markets. These can be slow, some claim to be fast. But if you want real long term air, the on board compressor is the way to go. This article will be about using a Sanden Compressor to achieve a fast, reliable compressor that will fill anyone's needs.

Most of us have older XJs with Sanden compressors. There was a change I believe in 96 to the Chrysler compressor on the air conditioning systems when they switched from R12 to R134 refrigerant. Either type of compressor can be used. How fast you can run the compressor depends on how you set it up.

The simplest way is to just drain the system and add an air filter and an air tool oiler to the intake hose and an air hose to the outlet. This works, but is not the best thing to do. These compressors will pump 400 psi and not even make the belt slip. I know they will do this because the pressure side of an AC system can run that much pressure. I really don't know what their upper limit is, but it is surely enough to explode an air hose or a tire. So there are things you need to add to the system to insure it functions like a real shop compressor. Also if you are using an air tool oiler for compressor lubrication, you cannot run it at high speed. You will have to settle for the engine idling only due to the heat the compressor will develop.

The first thing to know about a Sanden compressor is that it is a 5 piston, horizontal compressor. It was never designed to retain oil in the crankcase. It was designed to operate with oil suspended in the refrigerant, which is why there is a safety switch that will not let it operate without sufficient refrigerant in the system. So you need a lubricant. You can use an air tool oiler and let it operate at low speed and it will work. Or you can run oil in the crankcase and get some real speed out of it. But the pistons do not have oil rings like your engine does, so it will let oil escape into the compressed air. So it becomes necessary to make the system more complicated.

The first thing an air compressor needs is a tank. This allows the air system to operate without the compressor short cycling. Start ups are what is hard on anything, especially electric motors and compressors. So the tank stores air so the compressor can operate for longer times filling the tank and then shut off and cool in between. And unlike your shop compressor, the Sanden is designed to be cooled internally and has no external cooling. So it will get hot quickly.

IMG_0981.jpg


Viair makes several sizes of tanks. This one is a 2 gal. I mounted it in the back because there just isn't any room left under my hood. The nice thing about an air tank, it can be mounted anywhere, and with this one, it has a multitude of fittings so it can be mounted on or under something. And as you can see, that area behind it is a catch all for all kinds of things.

So now to compressor itself.

IMG_0073.jpg


IMG_0075.jpg


Here are my compressors. I did not want to sacrifice my AC in the hot summers we have, so I just added another one. If you can weld aluminum it is not hard to do. The jig I used was a plate bolted to the mount that had holes for the original compressor bolts and two more for the new compressor. Simple to make out of 3/8" steel bar stock. They you just start adding pieces to the original mount. Then I added an idler pulley I got at an automotive AC shop. For those of you that don't care about your AC, just use your current compressor. These compressors are available through hot rod vendors for just over $200 pus shipping. You will notice that there is stuff on top of the compressor on the left, the air compressor. We will address that later.

Next you will have to make a pressure hose for your system. The fittings on the Sanden compressor uses an O ring and does not resemble anything you can get at the hardware store. So what I did was use silver solder to braze a brass fitting to the steel fitting I cut off the original hose. To use it you must get the metals red hot and melt the silver solder on. There are several types you can get. This one does not corrode and turn ugly.

The next thing you will need for a proper system is a check valve.

IMG_0974.jpg


It only looks like a brass fitting here, but inside is a spring loaded ball pushed into a seat. This keeps the system from having air leak back through the compressor and also makes it easier for the compressor to start up, thus reducing wear.

The next item if you are going to run oil in the crankcase or an air tool oiler is an oil extractor. It is just a stone element that traps oil and lets it drip down into a bowl. This one has a site glass on it to see how full it is. If you run the air tool oiler, then you can just empty it periodically. But if you run oil in the crankcase, then you need a method to return the oil to it. There are two ways to do this. First is to take the bowl off and pull the plug in the top of the compressor and pour it it, or dispose of it and put fresh oil in the compressor. This particular oil extractor is available at Kilby enterprises

http://www.kilbyenterprises.com/coalescing-filter.htm

The brass screw in the bottom is tapped with 1/8" pipe threads so pipe fittings can be used. You can use a 1/4 turn valve in the bottom with a hose attached when the system is under pressure. When you open it the oil will be forced out and if the hose is attached to the top of the crank case, it will fill it. I got the fitting for the top of the crank case from Kilby also.

http://www.kilbyenterprises.com/oil-return.htm

However, I wanted something a little easier to use and I had some ARB solenoids laying around so I utilized a couple of them to be the valves for me. The first is put on the compressor itself.

IMG_0978.jpg


It is wired into the pressure switch along with the compressor clutch. When the compressor comes on, it opens and vents the crankcase thus not allowing pressure to build up in it and force oil into the air system, which it will do eventually. The second is on a line plumbed into the bottom of the bowl.

IMG_0973.jpg


It is somewhat difficult to see it all due to the amount of stuff in the way, buy here is the second solenoid. When the compressor shuts down and the system remains pressurized and the compressor vent solenoid closes, this one opens at the press of a switch and the oil goes from the bowl back into the crankcase.
 
So now on to the rest of the system, regardless of what you are doing for lubrication, to have a proper system you will need a manifold with a pressure switch and pop off valve. Here is my manifold.

http://www.kilbyenterprises.com/oil-return.htm

The first thing I want to discuss is the pressure switch. In the pic it is the brass thingy with the yellow wire attached to it. This is what determines what pressure your system will run at. It has a range. This one turns on about 125 psi and shuts off at 150 psi. That means that anytime the air system is less than 125 psi it will signal the compressor to come on by sending current to the little wire on the clutch, which will make the electric magnet in it pull the clutch plate into the friction material and the internals will begin to rotate. I chose a 150# switch because this compressor is fully capable of much more. Most systems are set up for less, around 100 psi. But my ARB air lockers are supposed to run at 95 - 105 psi, so I needed a system that ran a little higher to insure I had enough pressure at all times to operate them properly.

The other thing of interest on the manifold is the pop off valve. This is a safety device to keep your system from exploding in case the pressure switch malfunctions. I had one malfunction last year and I am glad I had it. It needs to be rated for a higher pressure than the shut off pressure of the pressure switch. So this is a 200 psi pop off valve. Still within what the hoses will take without damage. Here is a pic looking down from the top on the manifold.

IMG_0976.jpg


The last item on the manifold is the pressure regulator and ARB solenoids. The regulator is not necessary unless you have a reason to need a lower pressure, such as for the air lockers. It is set at 100 psi for them.

The last item is the high rev system. It should not be used unless you are using a compressor with oil in the crankcase You can buy a kit from Kilby for this, or you can make one for a few bucks. Here are the components I used.

IMG_0615.jpg


These parts are found on the 84 - 86 XJs with the 2.8L V6. It is a vacuum operated high idle system for when the power steering is under pressure. It normally only raises the rpm by 200 revs, but is capable of much more than that. The switch is located on the driver side fender well and has a wire that goes to ground and one connected to a pressure switch on the power steering line. I mounted it near my throttle body and is buried enough not to be visible to the camera. The vacuum motor is mounted on the throttle body.

IMG_0980.jpg


OK, lousy pic. But it pushes on the throttle and raises the rpm from idle to about 2700 rpms, which turns the compressor at above 5000 rpms. This provides enough air to air four 31X1050 tires from flat to 34 psi in under four minutes. It will cycle while filling, which means it maintains system pressure between 125 - 150 psi with the tires taking all the air they can with the valve cores in. I have not tried it without the cores in because at this speed I wouldn't gain anything time wise.
 
So now on to the rest of the system, regardless of what you are doing for lubrication, to have a proper system you will need a manifold with a pressure switch and pop off valve. Here is my manifold.

http://www.kilbyenterprises.com/oil-return.htm

The first thing I want to discuss is the pressure switch. In the pic it is the brass thingy with the yellow wire attached to it. This is what determines what pressure your system will run at. It has a range. This one turns on about 125 psi and shuts off at 150 psi. That means that anytime the air system is less than 125 psi it will signal the compressor to come on by sending current to the little wire on the clutch, which will make the electric magnet in it pull the clutch plate into the friction material and the internals will begin to rotate. I chose a 150# switch because this compressor is fully capable of much more. Most systems are set up for less, around 100 psi. But my ARB air lockers are supposed to run at 95 - 105 psi, so I needed a system that ran a little higher to insure I had enough pressure at all times to operate them properly.

The other thing of interest on the manifold is the pop off valve. This is a safety device to keep your system from exploding in case the pressure switch malfunctions. I had one malfunction last year and I am glad I had it. It needs to be rated for a higher pressure than the shut off pressure of the pressure switch. So this is a 200 psi pop off valve. Still within what the hoses will take without damage. Here is a pic looking down from the top on the manifold.

IMG_0976.jpg


The last item on the manifold is the pressure regulator and ARB solenoids. The regulator is not necessary unless you have a reason to need a lower pressure, such as for the air lockers. It is set at 100 psi for them.

The last item is the high rev system. It should not be used unless you are using a compressor with oil in the crankcase You can buy a kit from Kilby for this, or you can make one for a few bucks. Here are the components I used.

IMG_0615.jpg


These parts are found on the 84 - 86 XJs with the 2.8L V6. It is a vacuum operated high idle system for when the power steering is under pressure. It normally only raises the rpm by 200 revs, but is capable of much more than that. The switch is located on the driver side fender well and has a wire that goes to ground and one connected to a pressure switch on the power steering line. I mounted it near my throttle body and is buried enough not to be visible to the camera. The vacuum motor is mounted on the throttle body.

IMG_0980.jpg


OK, lousy pic. But it pushes on the throttle and raises the rpm from idle to about 2700 rpms, which turns the compressor at above 5000 rpms. This provides enough air to air four 31X1050 tires from flat to 34 psi in under four minutes. It will cycle while filling, which means it maintains system pressure between 125 - 150 psi with the tires taking all the air they can with the valve cores in. I have not tried it without the cores in because at this speed I wouldn't gain anything time wise.

The last thing is plumbing the air line. Mine is permanently fixed on the bumper. But exposed air chucks on the outside or under the hood can get dirt and grit in them. Mine is covered with a rubber boot, also available at Kilby enterprises or other vendors. I use a spiral wound air hose because it stores well in my goody bag.

IMG_0982.jpg
 
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