Topic: On Board Air
Written By: _peteyg

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Lots of times people ask me, "What is the first thing I should do to my Jeep? Should I get a lift and tires, do gears, buy lockers, get a winch, what?"

My answer is almost always, get On Board Air (OBA). I have had OBA on every wheeling rig I have owned, and I cannot imagine wheeling without it.

There are three basic types of OBA available today:

1 - Engine Driven OBA

The king of OBA is the engine driven compressor. You cannot beat an endless air supply, and it is the fastest air source available.

In the Engine Driven OBA world, there are two routes to go: Add a compressor, or convert your existing AC to on board air. The second choice is great if your AC already doesn't work, but if you want to keep the cold air blowing, like a lot of us do, then you will need to install an additional compressor. Luckily for those of us in the Jeep world, there is the Kilby On Board Air kit (http://www.onboardair.com). The Kilby kit is very well designed and made, and while expensive, it is the gold-standard for OBA kits. However, with a little bit of time and ingenuity, you can make your own brackets. The Kilby system is based on using a York AC compressor. You can buy the York brand new from Kilby, but it will be cheaper if you source one from a junkyard. They came in a wide variety of vehicles, but are most prevalent in late 70's Ford cars and trucks. You can also find them in older Volvos, Jeep Wagoneers and Full Size Cherokees, and even old AMC Eagle wagons.

While there are several different ways that you can set up your OBA system, there are some basic components that every engine-driven OBA system will (or should) have:

1. Pressure Switch
2. High Pressure Line
3. Intake air filter
4. Pressure guage (not necessarily needed, but highly recommended)
5. Air Tank (also not necessarily needed, but again, highly recommended)
6. Electrical relay for the compressor clutch power switch
7. Several feet of 10-gage wire
8. 2-pole on/off switch
9. Standard 5-pin automotive relay

Here's a really simple diagram of a trypical OBA system.


http://www.petesplace.net/auto/tech/onboar1.gif
Figure 1 - Simple OBA System Design

As you can see, the system is very basic, but could be easily expanded. Whether you go the Original AC or Add-a-Compressor routes, the basic design of the system remains the same.

There is a lot of research that should be performed before diving into this project, but it is not that difficult, and can be done in a day using simple hand tools. The biggest problem you will run into if you decide to source your compressor from the junkyard is finding a modern 5 or 6 groove pully instead of the old dual-V Groove pullies most comminly found on Fords. Kilby sells the correct pully for Jeep 4.0 motors. It's not cheap, but if you need it, he's got it.

I have built all three kinds of OBA systems. I have converted an existing AC system, built my own brackets, and currently I have the Kilby Bracket on my TJ. The Kilby system is by far the easiest solution if you don't want to convert your AC.

http://www.petesplace.net/petejeep/images/cj7_4sale/cj_oba2.jpg
Figure 2 - Pressure switch and manifold setup

http://www.petesplace.net/petejeep/images/cj7_4sale/cj_oba3.jpg
Figure 3 - York compressor on Jeep 4.2 using home-built brackets

There is no end to how handy having an unlimited air supply is, and I use my OBA every time I wheel. It is handy of course for airing up tires, but I find it is MOST useful for re-seating beads. The occasional use of air tools is good also. I carry my die grinder with me on big trips, and it always comes in handy. As an added bonus, if you isolate a portion of the system and regulate it down to 90 PSI, you can run your air lockers off it.

2 - Portable CO2 and Air Tanks

There are a few options available for portable air, with the gold standard being the PowerTank. The PowerTank works exceptionally well, and comes in a variety of sizes to meet every need and budget (yes, I used to write ad copy for 4WP) :flipoff2:

This is a more cost effective solution than a Kilby OBA kit, but it does come with the disadvantage of having to be refilled, and if you run out of CO2 at the wrong time, you could be left stranded. Additionally, although the up-front cost of the PowerTank is lower than the Kilby system, CO2 refills do cost money, so it has recurring costs after the fact. That said, the PowerTank is a quality system, can be moved from rig to rig, and is useful for power tools for short periods. While I have seen some people do it, it is not recommended to use a PowerTank for an ARB. If it runs out at the wrong time, you will suddenly be open. This could suck in the middle of, say, Wrecking Ball.

Other tank options include low cost air tanks that you charge up before you leave. These typoically are large and bulky, and do not really hold enough air to do anything more than squirt a few pounds of air into your tires before it runs out.

3 - Electrically Driven OBA
There are several options available for electrically driven OBA systems, with ViAir being the big brand name. Other options include the Sun Performance QuickAir systems, and a variety of others. These are mostly found in the mini-truck world, and are painfully slow. However, they are reliable, and in some cases much cheaper than the PowerTank or Kilby systems. For people looking to get OBA on a budget, electrically driven compressor can provide a workable solution.

OK, guys! Have at it! If you see things I missed or have another idea for how to set the system up, post up!

Great write-up!

I woudl add to that to really benefit froma engine driven OBA, a tank should have a minimal of 3-5 gallons for air tools.

Another note is that the OBA is a way better air setup for air lockers than the small electric compressors. Just add a regulator, and switch and will perform very well.

An often overlooked idea for some Jeeps is teh use of the existing Sanden compressor. Or for rigs without AC, it is almost a bolt on affair once you obtain teh compressor as several non\ac Jeeps already have the bracket in place ready to bolt teh compressor. This woudl requrie basically a longer serpentine belt and the compressor itself along with teh parts mentioned above. They do work well, but do not have the same flow as a high capacity York, or internal lubricatin, so an inline oiler woudl be needed. Still it is a hard to beat, inexpensive and easy option.

Great write-up!


An often overlooked idea for some Jeeps is teh use of the existing Sanden compressor. Or for rigs without AC, it is almost a bolt on affair once you obtain teh compressor as several non\ac Jeeps already have the bracket in place ready to bolt teh compressor. This woudl requrie basically a longer serpentine belt and the compressor itself along with teh parts mentioned above. They do work well, but do not have the same flow as a high capacity York, or internal lubricatin, so an inline oiler woudl be needed. Still it is a hard to beat, inexpensive and easy option.

Thanks!

Sanden's make very good compressors, and in fact I have a converted Sanden on my Scrambler. The compressor was a leftover from the XJ drivetrain I put in it, and it works very well. I learned from a friend a long time ago that you can get away without an inline oiler for a Sanden if once a month or so you squirt DuraLube through the compressor while it is running for about 30 seconds or so. I have been using this method with great success ever since.

In the case of my TJ, my factory AC still works, and even though it's a trailer queen, in the summer I like to put the top on and run the AC on hot days, just so I can drive it around. It is very nice to have both a functioning AC system and OBA, although I'll admit it is a little blingy.

Could expand on the Electric compressor oba system to include a wiring diagram and maybe include the common part #'s for the pressure switches most people use when running a tank with an electric compressor.

Could expand on the Electric compressor oba system to include a wiring diagram and maybe include the common part #'s for the pressure switches most people use when running a tank with an electric compressor.

Really, there's nothing different about the wiring on an electrical compressor. Instead of turning on and off the magnetic clutch for the AC compressor, just turn on and off the motor.

For the pressure switch, I like to use these:

Square D FHG12J52XBP Air Compressor Pressure Switch (http://www.acehardwareoutlet.com/(30l3weuubc4awdvlhdvyqaqv)/productdetails.aspx?sku=998033791)

Here's one installed in my Scrambler:

http://www.petesplace.net/gallery/albums/userpics/10001/IMG00115.jpg

I use teh similar ones form Grainger, about the same setup.

One other thing I would add to the diagram is a mechanic pressure release valve. About $5 but great insurance in case the pressure switch fails or teh pads lock up. Basically it will let air out of the system at a predefined PSI, i.e. 150 or 200 psi. Thsi will save harm to the compressor, lines, tank, etc. It will also allow quick manual release of teh system when needed:

http://www.greenpowerscience.com/STEAMBOILER/DSCF6724.JPG

I use teh similar ones form Grainger, about the same setup.

One other thing I would add to the diagram is a mechanic pressure release valve. About $5 but great insurance in case the pressure switch fails or teh pads lock up. Basically it will let air out of the system at a predefined PSI, i.e. 150 or 200 psi. Thsi will save harm to the compressor, lines, tank, etc. It will also allow quick manual release of teh system when needed:

http://www.greenpowerscience.com/STEAMBOILER/DSCF6724.JPG

Weld a bung for this in the bottom of the tank and use it occasionally to evacuate water from the system (unless you have an air dryer, then the location would not be as important).

I will actually argue against a mechanical blow off valve.

In colder climates, I have had mine blow several times below rated PSI and not reset.

maybe you had a crappy blow valve? I never had anyissue with the ones I used, and the rigs have seen plenty of snow withoiut any issues.

I believe some York's have a built in mechanical release valve. How I found out? Well once I installed my check valve backwards :D...

maybe you had a crappy blow valve? I never had anyissue with the ones I used, and the rigs have seen plenty of snow withoiut any issues.

I believe some York's have a built in mechanical release valve. How I found out? Well once I installed my check valve backwards :D...

I did that once....the release is actually a blown head gasket. Yorks are really cool when you pull them apart. Look just like a little engine.

I need to check on that. It actualluy looks like a blow valve on the body of the York I had.

I will actually argue against a mechanical blow off valve.

In colder climates, I have had mine blow several times below rated PSI and not reset.

The blow off should be about 25 to 30psi higher than the max air tank pressure. If your air tank is rated to 150, the pressure release valve should be rated to 175.