…and yet another On-Board-Air (OBA) write up? There are so many write ups out there already, why write another one? When I was doing the research about my set-up, I must have read at least 10 different excellent write-ups all doing the same thing but all a slightly different way. From each write-up, I always found one little detail that I liked and wanted to use. Some features I did not use but it made me think of something new or helped me solve a problem. Sooooo here is mine and I hope what I have done and my lessons learned will provide whomever is reading it that one additional detail or feature or approach that may help them complete their system.

The Air Compressor

I have a Sanden air compressor already installed in my Jeep. The freon had already been removed (leaked out) and I was in the process of removing all the associated hoses and hardware when my friend told me to convert it to an OBA system. Unfortunately, I had already removed the hoses directly attached to the compressor and had thrown them away. I had to take a couple trips to the junkyard to find the fittings that fit.

Since freon was originally used to provide the lubrication, I needed an oiler to keep the unit lubed. I also needed an air filter to keep larger air born matter out of the compressor. I bought both items at Home Depot. At the output side of the compressor, I installed a filter to remove moisture. I also got this at Home Depot.

I attached 3/8 ID high-pressure hose the output of the moisture filter and ran it towards the firewall. Here I installed a check valve to prevent loss of pressure back through the air compressor. After the check valve, I installed a brass “T” fitting. One side of the “T” ran to my air tank and on the other side, I ran 1/8” ID high pressure (thin red hose in picture) hose through the firewall terminating behind the dash.

The Dash

On the dash, I installed a pressure gauge to tell me to what PSI my system was charged. Also on the dash I installed a toggle switch to turn the system on and off. Behind the dash I installed my pressure switch to turn off the compressor when the system pressure reached 120 PSI. Both the pressure gauge and the pressure switch are fed by the 1/8” ID red pressure hose that came in through the firewall. My toggle switch was connected to 12VDC through a 10 amp fuse from my fuse panel and was tied in series with the pressure switch.

The Tank

I installed the tank on the floor behind the front seats in the foot well for the rear passengers since I removed the rear seat for additional storage.

On the tank I installed 2 air chucks and the emergency pressure switch. The pressure switch is set to release pressure at 150 PSI.

The tank is fed from the pressure hose coming from the “T” brass fittings in the engine compartment. From the engine compartment, I ran the hose under the tub and tie wrapped it to the frame.

I drilled a hole under the tank and fastened my hose coming from the engine compartment to the tank with a quick disconnect fitting.

The Wiring

I installed a relay and powered it from the fuse panel – through a 10 amp fuse - through my toggle switch on my dash – through the pressure switch behind my dash – through the firewall to the relay mounted in the engine compartment. The power to the air compressor clutch came directly from the battery – through a 10 amp fuse - through the relay – and to the air compressor clutch wire.

There is no return line from the compressor. The unit is grounded to the chassis for the return path to the battery.


The Schematic

Lessons Learned

Lesson # 1. I probably did not need to use the relay. When I first wired it all up, I had the power going from the fuse panel – through a lighted toggle switch – through the pressure switch – directly to the compressor clutch wire. It didn’t work. There wasn’t enough juice to grab the clutch. I figured there was too much resistance through my wiring so I installed the relay. After I did this, it still didn’t work. The lighted toggle switch was my problem. The voltage drop across the switch took all my juice. Once I replace the lighted toggle switch with a regular switch, everything worked and since I already had the relay hooked up, I didn’t bother to test the system without it.

Lesson # 2. I’ve heard/read that I didn’t need the check valve with the Sanden compressor. I don’t know this for sure. Anybody using this compressor may want to look into this further.

Lesson # 3. I attached the moisture filter directly to the output of the compressor. The air coming out of the compressor is VERY HOT and I had a difficult time keeping the hose clamped on. I had to put a second clamp to keep the hose from blowing off. When I get around to it, I’ll be moving the filter further down line nearer to where the check valve is. This will give the air a little distance in which to cool off. I’ll also be using a factory clamped hose to the output of the compressor.

Lesson # 4. Don’t throw away the input and output fittings for your compressor.

Lesson # 5. You can buy everything you need at http://www.onboardair.com

Lesson # 6. You can get any question you want answered at http://www.jeepsunlimited.com

Future Mods

Mod # 1. I’ll be installing a hand throttle to keep my engine RPMs higher to keep the air coming through faster.

Mod # 2. I may move the tank below the tub in front of the gas tank. The kids are getting older and want to ride with me.

Mod # 3. I’ll be installing a drain cock on the air tank.

Mod # 4. I may build a big rear bumper and use the inside as an additional air tank. If I move the existing tank below the tub, I’ll need a new place to install my air chucks and they may go on the new bumper.

Mod # 5. Move the moisture filter farther away from the output of the compressor.





If you have any questions, please feel free to e-mail me at

georgeteding@yahoo.com