How-to: Install On Board Air (Air Compressor, Tank, & Air Horn) **PIC HVY***

Yellowjacket Gets Lungs (1/23/2013)

Over this past MLK weekend, I decided to tackle the box of parts that had been sitting in my garage, and install the on board air and air horn in my XTerra.

PARTS BOX

Parts I Used:
1 VIAIR compressor
1 2.5gal air tank
1 110/145 PSI pressure switch w/ relay
1 “Cicada” semi-truck style air horn
1 pressure gauge with relay switch
50’ 1/4” ID air line tubing
8’ nylon gauge line
3 NPT “T” fittings
1 F/F NPT connector
3 hose end “repair” kits with compression fitting to NPT connector
10 gauge wire with inline 30A fuse (compressor power supply)
1 large computer fan
JB Weld

The first thing to do was to decide where to mount the on board air equipment. A lot of people seem to use the engine bay or chassis, but I decided it exposes the compressor to heat and moisture, so I elected to take an idea from THIS THREAD by Macguyvermedic, and install the compressor over the right back wheel well. There’s a pretty good void space there, and there are already vents built into that side trim panel in the cargo area, minimizing the modifications I needed to make. The only downside is removing the trim panel. It’s a little involved, involving complete removal of the cargo tray and unbolting the rear passenger seat belt.

VOID SPACE BEHIND CARGO PANEL

By far the biggest piece of the system is the 2.5 gallon air tank. It’s too big to fit anywhere on under the hood or chassis without relocating the spare. After some careful thought, I decided to mount it in the cargo area for easy access and protection from the elements. I test mounted it to the same trim panel I removed to install the compressor, and was happy with the result:

FITTING THE TANK

The next piece was figuring out where to put the horn. My biggest desire was to keep it hidden if possible. Luckily, I discovered the space behind the front bumper was a perfect fit for the horn, and should protect it from most of the dirt and direct moisture impingement. Pics of that later.

The VIAIR kit comes with a thin diameter rigid plastic hose that I found balky and awkward. I was also concerned about airflow to the horn through that tiny hose, since there is about 17’ of hose between the tank and the air horn. Because of all that, I elected to run flexible blue 300psi-rated NPT-fitted hose through most of the system. This changed the fitting requirements from the kit somewhat, so a trip to Home Depot was in order.
Once all the parts were in hand (or so I thought), I began by fitting that 2.5gal tank to the cargo trim panel. I drilled holes and added a quick-disconnect fitting to the filler hose, which allows for easy removal of the panel and tank assembly if I need to make repairs or modifications in the future:

TANK MOUNTED ON PANEL

I also added a cooling fan, to force some ventilation to the compressor, especially in the heat of summer. Macguyvermedic’s install used a switch to control the fan, but I decided it would be more elegant to wire it directly into the relay circuit for the compressor, so the fan kicks on and off with the system.

FAN DETAIL

Time to mount that compressor! I had trouble marking the holes for the base, so I borrowed yet another idea from Macguyvermedic, jacked up the truck, and marked & drilled the holes from underneath. That made things super-easy, and the compressor was mounted.

COMPRESSOR IN PLACE

I used RTV to seal the bottom of the bolts to keep moisture out of the compressor compartment.

BOLTS IN WHEEL WELL

Next, I began to wire up and run grounds from the compressor and pressure switch/relay unit. I also put some fittings together and created a small “H” shaped manifold. The four fittings go to the compressor supply, the pressure switch, the tank line, and the final one is for the line going up front for the pressure gauge and air horn.

H-AIR MANIFOLD

Time to run lines and wires! Below are a couple of shots running the lines forward, and an additional T-fitting under the passenger seat carpet where the gauge line branches off the horn supply line.

RUNNING LINES UP PASSENGER SIDE

The yellow wire is for the relay switch which I installed with the gauge by the driver’s right knee. I also ran the primary power wire directly back from the battery terminal. The 10 gauge wire has a built-in 30A fuse to protect the system.

BATTERY DETAIL

The supply line from the T-fitting by the passenger seat had to go up front for the horn, so rather than drill through the firewall, I elected to drill through the bottom of the X near the frame, and run the line and power supply wire through there. I secured the line and wire on both ends, and padded the hole to minimize rubbing issues.

WIRES THROUGH BELLY

The line for the horn was run along the frame to the right front fender, up and over the wheel in the outer part of the fender, and into the front bumper. Since I had to remove the fender trim screws, I also took the opportunity to permanently remove my mud flaps.

Now with all the air lines and wiring run, it was time to re-install the cargo trim panel with the attached tank.

TANK/TRIM PANEL HOOKUP

TANK ON RE-INSTALLED PANEL

Next, I connected and wired up the gauge and trigger switch...

GAUGE DETAIL

And installed the air horn and honk button (momentary contact switch). I accidentally blew the power plug fuse when wiring up the horn switch, so the horn and my CB didn’t work when I was done. D’oh! ***This is a reminder to disconnect your battery when you work on electrical stuff, especially if you’re tapping into or modifying existing wires.***

HORN IN FRONT BUMPER

HORN BUTTON

With all that done and one 20A fuse later, it was time to pressurize the system for the first time. The relay trigger switch is wired to the accessory power circuit (via the upper dashboard power plug), so the compressor literally cannot drain the battery unless I’m dumb enough to let it run with the key in and the engine off. In order for the compressor to run, 3 things must be true:
1.) Key in ACC or RUN position
2.) System pressure below 110 psig
3.) Compressor switch set to ON

The compressor makes a little noise, but it isn’t overpowering. You can still carry on a conversation or listen to music at a reasonable volume from the front seat with the compressor running. It would probably be slightly unpleasant for anyone sitting in the back right seat however. Fortunately, it takes less than 5 minutes to pump up the system from zero, so with all the leaks sealed, it shouldn’t have to run much unless I’m using the system to inflate tires.

PUMPING UP THE SYSTEM

Now that I had pressure, guess what I found? Leaks. The swivel on the back of the tank was leaking heavily, so I ended up replacing it with a straight quick-disconnect fitting so I can still plug in an inflator hose or air tools back there. I also tightened all the fittings on the tank and the T-junction by the passenger seat and sealed the audible leaks there. Finally, the air horn itself was leaking at the base of the factory-installed nut. I removed it, put sealer on the threads, and re-installed the nut. Still leaked around the base- infuriating! So with the system depressurized, I JB welded that nut to the horn. That had better fix it! My goal is an air system that will maintain pressure overnight to avoid running the compressor constantly. The “H” manifold behind the trim panel is probably leaking too, but the leak isn’t audible, so I am waiting until I’m more motivated to start ripping the trim apart again to check and fix it.

This install was done over 5 days, working between 4 and 6 hours per day as I wanted to enjoy the weekend with my family and not be slaving away in the garage the whole time. The horn sounds GREAT, and I’m glad I retained the factory horn as my default. Having the system well hidden is nice, too- this OBA system about as stealthy as I could make it. Aside from seeing the tank through the cargo area windows, the only outside indication I have onboard air is this decal:

VIAIR DECAL

This was a time-consuming install, I hit lots of snags, made multiple runs to Home Depot, Wal Mart, and Staples (for the fan), thought seriously about throwing in the towel once or twice, and finally got a huge grin on my face when I honked the air horn for the first time. Comments are welcome, but I’m happy with the way this turned out. Kudos to Macguyvermedic for some great ideas that got me rolling with this mod. If anyone wishes to attempt anything like this, feel free to PM me or post here with questions.

Thanks for reading!

How-to: Install On Board Air (Air Compressor, Tank, & Air Horn) PIC HVY*

SycoCell

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