- It's pretty simple once you figure it all out but there are a few points to consider.
The compressor, in-line filter, unloader/check valve, pressure switch, pressure gauge, air tank & drain valve, safety valve, and of course the air hose and fittings.
The diagram to the right shows the layout of everything I used for the OBA system.
- I'll briefly describe what I've done for each of the above here:
- [ compressor ] Older CJ's that came with A/C used York compressors so that's what I decided to use. The bracket was easy to come by and so was the compressor. They cost about $50 from a local pull-a-part yard.
- [ in-line filter ] I'm using this to catch any oil coming through the line from the compressor.
- [ unloader/check valve ] This has two functions. First, once the air goes past the check valve it can't come back towards the compressor. It basically makes it a one-way street. Second, it unloads any pressure from the compressor side of the valve. I don't really understand how/why this part of it is needed but I think it has something to do with backpressure in the compressor. For whatever reason, most people said it was good to have so I added it too.
- [ pressure switch ] If you want to just turn on the compressor when you want, a simple wire and on/off switch would work ok (maybe) and you won't need this. Most other people, including me, wanted it to be somewhat automatic so whenever the pressure in the system goes below 95psi it will turn on, and when the pressure reaches 125psi it will turn the compressor off. I have a simple on/off toggle switch mounted to the cover of the pressure switch. When it is on (live), it makes the relay live, which then makes the pressure switch live. Now the system is completely live and ready for the pressure switch to sense pressure under 95psi. When it does, it's lead to the compressor engages the clutch on the pulley shaft, which then makes the compressor pulley spin, which then feeds air through the output line of the compressor. When I'm finished airing up or whatever, I turn the switch off which then cuts power to the entire system so the compressor clutch can't engage. If it did engage the compressor clutch while the Jeep wasn't running, it would drain the battery (trust me on this).
- [ pressure gauge ] I mounted this on my dash so I could see it whenever I was in the Jeep. I liked that idea better than just mounting it under the hood, on the tank, or wherever else that wasn't visible without getting under something. Its range is from 0 to 160psi
- [ air tank & drain valve ] Having an air tank is a good idea because it gives the compressor some working volume to fill up when it's running. With that volume, and a 30psi range (from 95-125psi) you can run air tools, air hose or anything else that runs using air. When my tanks are full I start airing up, which decreases the system pressure, then the compressor kicks on and starts filling the tanks back up while I'm emptying them into my tires. After looking at the 'real' tanks offered by various off-road suppliers I decided $75 was too much to pay for a 2.5 gallon tank. One of the other sites I was checking out mentioned using air-brake tanks from semi-trucks instead. So, that's what I looked for. I wound up getting two, basically just because I could since there was a lot of room under my CJ-6. They're 9" in diameter and 13" long, a little over 3 gallons each, came with really good mounting straps and only cost $40 for the pair. They also had a port to attach a drain valve on the bottom of the tank. They actually had 5 ports in all for each tank but I just plugged the ones I didn't use.
- [ safety valve ] You need this in case your pressure switch fails to disengage the compressor clutch or some other system failure, and the compressor just keeps producing air into an enclosed system. Mine is set to blow at 150psi so if the system pressure gets to that point, it opens up and releases the air pressure until it gets back below 150psi. It could be mounted just about anywhere in the system but I decided having it accessible without being under the hood was better, and feeding off the passenger tank was as good a place as any.
- [ air hose and fittings ] I used 3/8 hose with a 300psi strength rating. The fittings are all brass and I used solid band clamps instead of regular hose clamps with the holes in the side. I found the regular hose clamps would strip and not hold very tight while the solid clamps have much greater holding strength to them. I also added a shutoff valve to the line feeding the air tanks. This isn't really necessary but I figured why not. It might come in usefull sometime. Of course that's what I say about almost everything in my garage, so use your own judgement on this.
- The first picture shows the York compressor I used.
- The last picture shows one of the two air tanks I used. I got them from a semi-truck salvage yard. It cost $40 for both 3.25 gallon tanks, including the mounting straps. The tanks are 9" in diameter, 13" long, and a whole lot cheaper than the 'real' air tanks sold by offroad suppliers. They had two 1/2" ports front and back, and a 3/8" drain port on the front. I plugged the two ports in back, and the side ones on the front of the tanks and installed drain valves into the lower front ports. They also came with removable straps which are used to mount them to the vehicle. Using these, I can just remove the two strap bolts and the tanks come right out if I need to remove them for any reason.
- The first picture is after I installed the compressor mounting bracket. I picked it up at a junkyard off a Wagoneer that had A/C in its previous life for about $10 (in the picture, it's just above and to the left of the radiator reservoir). You can also see the flexible radiator hose I had to get since I couldn't find a hose for a CJ-(with a/c) at any parts stores.
- The next two pictures are after I installed the compressor.
- The first picture is after I installed the compressor mounting bracket.
- The next two pictures are after I installed the compressor.
- The first picture shows a view from the passenger side of the Jeep. The first line split from the manifold feeds into the pressure switch. The pressure switch is wired to the compressor and engages the compressor clutch when the air pressure in the system falls below 95psi. It then releases the clutch when the pressure reaches 125psi. I attached the relay to the bottom of the pressure switch, and the main on/off switch to the front of it. The on/off switch disconnects power to the pressure switch so it doesn't engage the clutch while the vehicle is parked, or when you don't want the compressor running. NOTE, if you leave the switch on and the system pressure falls below 95psi, it will engage the clutch. If the vehicle is parked overnight, the compressor won't be running of course because the engine isn't running. But, the current used to engage the clutch is enough to drain your battery if left on. Therefore, this little master switch is absolutely required. Most of the layouts I've seen have the switch mounted in the dash, but to keep anyone (or me) from turning it on accidentally I installed it in the engine compartment, directly onto the pressure switch.
- The middle picture shows a view from the driver's side of the Jeep. The second line split is for the hose that runs to the pressure gauge I have mounted onto the dash in the cab. The last split runs to the dual air tanks I have mounted under the Jeep. I put a shut-off valve in the line so I could seal off the tanks if I needed to work on any of the lines or connections upstream from this point. Although, it only takes about 75 seconds for both tanks to reach 125psi from empty so it wouldn't really matter if they lost pressure for maintenance or whatever. The manifold then feeds a line to the quick-disconnect I have mounted on the driver's side fender under the hood.
- The last picture shows an overall view of the manifold and firewall.
- The first picture is of the quick-disconnect mounted to the passenger side fender under the hood.
- The second picture is of the quick-disconnect mounted to the driver's side fender under the hood.
- The next picture is of the passenger side air tank. The source line comes in from the driver's side air tank to the right. It then feeds into a 'T' which splits to the 150psi safety valve at the bottom, and the top goes to an elbow, then to the reducer nipple which screws into the tank.
- The last picture is of the driver's side air tank. The source line comes in from the right, to an elbow under the 'T'. The 'T' then splits a line left to the passenger side air tank, with the top of the 'T' going into an elbow, then to the reducer nipple which screws into the tank.
- The first picture is of the pressure gauge mounted on the dash. I was hoping to find a flush-mount gauge but couldn't find a small one in time to complete this. I'll find one eventually and install it later.
- The last picture shows the line coming from the compressor to the unloader/check valve, then the inline filter, then a 'T'. The 'T' splits left to the passenger side quick-disconnect, and right to the manifold and pressure switch.
- All three of these pictures show the passenger side air tank mounted to the Jeep, before mounting the driver's side air tank.
- They also show how much room there is under the bed of a CJ-6.
- The first picture is a rear view of both tanks after installation.
- The other three pictures show various angles of the air tanks from the front.
www.nacs.net/~djperk/Jeep/tech/oba.html
home.europa.com/~bateman/jeep/78cj5/mods/air/index.html
www.huv.com/jon/jeep/Air/index.html
users.supernet.com/luv2jeep/on-board.html
www.off-road.com/jeep/tech/body/york
www.harryworld.com/harry/york.html
www.jedi.com/obiwan/jeep/yorkair.html