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Installing a Compact Air Compressor that Fills a Tire in 90 Seconds

Posted in How To: Wheels Tires on July 19, 2017
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A source of compressed air is essential when venturing off-road. Inflating tires using CO2 tanks is quick, but tanks have a limited supply. Portable compressors are simple, but take a long time to fill four tires. These limitations make a permanently mounted, high-capacity air compressor a particularly compelling option. Combining the ability to quickly fill a tire with an endless supply of air makes a high-flow compressor a great solution.

Focusing on performance at a useful, tire-filling 30 PSI, the familiar brands offer some worthwhile choices. Two of the major manufacturers, Viair and ARB, offer good products; but Viair offers a 1.86 cubic-feet-per-minute (CFM) single-cylinder compressor, and ARB offers a 2.34 CFM single or 4.68 CFM double-cylinder compressor. Although Air-Zenith (AZ) is not as well known in the off-road world as Viair or ARB, its AZ OB2 air compressor can produce 4.25 CFM from a single cylinder, and pressure up to 200 psi at a 100 percent duty cycle. Key to this ability is large cooling fins on both the cylinder and cylinder head, and an electric cooling fan on the cylinder head. This second-generation design is very robust, providing high reliability under constant use. The OB2 was developed for the air suspension market, which tends to put more hours on a compressor than off-road customers do, and the entire compressor and motor can be easily disassembled and rebuilt with spare parts available from the manufacturer, if necessary.

The basic AZ OB2 compressor comes with a stainless steel braided leader hose, wiring harness, and relay.

In order to evaluate the compressor it was installed on a Jeep JK Wrangler Unlimited Rubicon. Your selection of a mounting location should take into account accessibility as well as environment. While a compressor can be mounted under the vehicle or in the engine compartment, those locations can be wet, muddy, dusty, or hot. Those conditions are enemies of a compressor’s performance and lifespan. In the JK Wrangler there is enough room under the passenger seat for a compressor, which is a clean and cool environment. This location gives access to the air at the passenger door, and is also relatively close to the battery so wiring for power is short and convenient.

Air-Zenith offers a complete kit, including compressor, hose, wiring, and air tank. However for our application, the tank was not needed. Ordering the compressor alone still included the basic wiring harness, relay, and leader hose. Additionally ordered were an 80-amp fuse and holder, a master switch, a pressure switch, and an air manifold.

Installation was fairly straightforward. The passenger seat was removed to access the mounting location and the compressor was mounted to the floor. Wiring and plumbing were then completed. The details are shown in the photos.

How did it perform? While the compressor made noise while running, it was not an objectionable frequency or sound level. With the engine running, we measured it at 80 db at the driver’s location, compared to 52 db with the compressor off. Current draw was less than 30 amps at 40 psi. Voltage drop at the compressor was only 0.22 volt while running, indicating the wire size is appropriate for the length and amperage. As far as inflation performance, a factory 32-inch tire was inflated from 15 to 30 psi in 90 seconds. While your Jeep’s tires are likely larger, it’s doubtful they would take too much more time to refill after a day of wheelin’.

The installed compressor was out of the way but offered easy access to the power switch and air coupling. Filling a tire is now a simple process of plugging in a hose and flipping on the switch. Follow along as we show you how it was done.

Easily found at your local hardware store, 6- and 16-gauge wire and crimp lugs were used for this installation; and although we got ours from T-Spec, an 80-amp MANL fuse and distribution block can be found online or at car stereo stores.

Tool List

Wire cutter/stripper/crimper
Soldering iron
Socket wrenches—13 & 18mm
Open-end wrenches
Rivet nut installation tool
Power drill

Parts List—Estimated Cost: $400

Air-Zenith AZOB2K Compressor
Air-Zenith pressure switch
T-Spec 80 Amp fuse
6-gauge wire, 7 feet
16-gauge wire, 5 feet
Electrical toggle switch
Assorted crimp lugs, shrink sleeve, screws
Rivet nuts
3/8-inch FPT manifold or T, and 3/8-inch to 1/8-inch reducer
Air quick disconnect coupling, 3/8-inch MPT x 1/4-inch I/M

Our first step was to remove the front passenger seat. Four 18 mm bolts hold the seat to the floor and six 13 mm nuts hold the base to the seat. There is one connector under the seat to disconnect. The seat can be moved back and laid on the rear seat.
The carpet was lifted and the seat base placed back on the floor. We then determined the mounting location of the compressor. Check for adequate clearance between the seat and compressor, and compressor and floor. Plan the routing of wire and air hose. Mark and center-punch the hole locations.
Holes for the rivet nuts were drilled. Check underneath the floor before drilling to ensure there is clearance for the rivet nut installation and that you won’t damage something underneath. The gas tank is near the front two holes. Be safe and slip a piece of plywood underneath to prevent the drill bit going too deep.
The rivet nuts were installed next. We used Rivnut-brand 1/4-20 thread. You can find rivet installation how-to videos on YouTube if you’re not familiar with the procedure.
Holes were then cut in the carpet for the installation locations, and the carpet was put back in place. In this case we installed studs with Loctite in the rear, and a 1-inch-tall spacer in front.
The compressor was installed on the studs and spacer. The spacer compensated for the uneven floor and kept the potentially hot cylinder away from the carpet.
The AZ ground wire was then installed on the existing ground stud near the center console.
An 80-amp MANL fuse holder was mounted to an existing stud near the battery, and wire from the fuse was routed below the battery to join a factory wire harness that passed through the firewall. Caution: Do not connect to the battery until all other connections are complete.
Under the glovebox the factory wire harness can be seen in the corner. We ran the red 6-gauge wire through the existing rubber seal with the factory harness. It was easier to push the wire through the firewall from the passenger compartment side. To the rear it was routed behind the plastic trim piece and under the seat.
These components control the compressor. The master switch enables power. The pressure switch cycles on at 85 psi and off at 105 psi. The relay controls high amperage to the motor. They were wired in series with 16-gauge wire. The switch is a sealed toggle with safety cover.
The air from the compressor supplies the quick coupling and a pressure switch. This can be done with a commercial air manifold or simple plumbing tee. In this case we fabricated one from a block of aluminum. Two 3/8-inch FPT holes and one 1/8-inch FPT hole were drilled and tapped in a “T” configuration. This block was mounted to the seat base.
The pipe thread fittings were installed on the manifold using Teflon tape. A bracket was added to mount the power switch. The AZ braided hose uses military 37-degree flare fittings for easy installation.
With the seat base and compressor in place, the wiring was completed. The air hose was installed between the compressor and manifold by tightening the nuts. No Teflon tape was needed on these connections.
A distribution block was used to connect wires with the main 12v power from the battery. The lugs were crimped on the wire, soldered, and then shrink-sleeved. The Air-Zenith relay was collocated with the distribution block to minimize wire length.
The air manifold and power switch were mounted under the seat base using existing holes near the passenger door. Then the wires to the switch and pressure switch were installed.
After double-checking all the wire and plumbing connections, the main power wire was attached to the battery using an existing terminal.
With the seat reinstalled, the completed installation allows plenty of clearance for the compressor. A plastic shield will cover the 12V distribution block.
The air coupling and switch are accessed from the passenger door. Tire inflation is now an easy task.

Amazon Affiliate links are our attempt to show you real-world pricing and availability for the products we review and install, and while the Amazon links are separate from editorial and advertising, the Four Wheeler Network may receive a commission on purchases made through our posts.


Las Vegas, NV 89118

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