Air Locker Install Guide: Onboard Air Setup 2026
Fitting an air locker is only half the job. The onboard air system behind it decides whether the locker engages the instant you flick the switch or hesitates for a few seconds right when you need traction most. This guide walks through building that support system in the correct order: compressor, tank, plumbing, pressure control and wiring.
Why this matters
An air locker works by using compressed air to push a piston that locks the differential. No air pressure, no locking action — the mechanism itself is simple, but it depends entirely on what feeds it.
A lot of DIY installs get the locker fitted correctly and then throw the air side together with whatever compressor was lying around. A weak 12V compressor, an undersized tank, and wiring run off an accessory fuse are the three most common causes of a locker that hesitates or won't hold engagement under load in 2026.
The fix isn't complicated. It's a compressor rated for the job, a small air tank to buffer demand, a pressure switch or controller to manage cut-in and cut-out, and wiring that can carry the current without voltage drop. Boss Air Suspension supplies the onboard air side of this setup — compressors, aluminium tanks, controllers and fittings — and this guide covers where each part goes and why. For a broader look at pairing tank size to compressor output, the onboard air system guide for air lockers goes into more detail on sizing.
What you'll need
- A 12V air compressor rated for continuous duty — a compressor such as the PX01 12V air compressor suits a single-locker circuit
- An aluminium air tank to buffer demand — a 2 gallon 3-port tank is enough for one locker; step up in size for dual-locker vehicles
- A pressure switch or digital controller to manage cut-in and cut-out pressure
- Push-to-connect air fittings, a water trap and 1/4 inch air line
- A relay, fused wiring loom, ring terminals and a dash switch
- A drill, wire crimpers, a multimeter and a pressure gauge
- 60 to 90 minutes per locker circuit — longer if you're wiring dual lockers
The steps
1. Mount the compressor
Pick a location with airflow and protection from water and dust — under the tray, behind a wheel arch liner, or a dry corner of the engine bay away from exhaust heat. The compressor needs to breathe to avoid overheating on longer fill cycles.
Secure it with rubber isolation mounts to cut vibration noise. Common mistake: mounting low near the diff or chassis rail without water protection, which leads to corrosion inside the housing within a season of Australian dust and creek crossings.
2. Mount the air tank
Position the tank close to the compressor and reasonably close to the locker plumbing run, with the drain point facing down so condensation can be released. A tank mounted level and accessible makes servicing far easier later.
A 2 gallon tank gives one locker a reasonable buffer between compressor cycles. Common mistake: tucking the tank somewhere the drain valve can't be reached without removing panels.
3. Plumb compressor to tank
Run 1/4 inch air line from the compressor outlet through a water trap into the tank inlet. The water trap catches moisture before it reaches the tank and, eventually, the locker solenoid.
Build pressure slowly the first time and check every joint with soapy water before moving on. Common mistake: skipping the water trap — moisture in the line is the single biggest cause of locker solenoids sticking over time.
4. Install the pressure switch or controller
The pressure switch decides when the compressor kicks in and cuts out. Set the cut-in point low enough that the tank never runs near empty, and the cut-out high enough that there's margin above what the locker needs to engage reliably.
A controller such as Boss Air Suspension's auto pressure controller kit combines the switch, fittings and water trap in one unit, which simplifies this step considerably. Common mistake: setting cut-out too close to cut-in, which shortens compressor life through constant short cycling.
5. Run the air line to the locker solenoid
Route the line away from heat sources, moving suspension components and sharp chassis edges. Secure it with clips every 300mm or so and leave a small amount of slack at any point the suspension articulates.
Common mistake: running the line tight across a control arm or leaf spring — articulation will eventually chafe through the line at the pinch point.
6. Wire the electrical circuit
Run the compressor feed direct to the battery through a relay and an appropriately rated fuse, not off the accessory circuit. Thin wiring and shared circuits are the top cause of slow-fill complaints.
Add a dash-mounted switch for the driver, wired to trigger the relay rather than carrying compressor current directly. Common mistake: using automotive-grade wire that's undersized for the compressor's draw, which causes voltage drop and a compressor that struggles to reach cut-out pressure.
7. Pressure test and adjust
Build the whole system to around 90 psi and check every fitting again with soapy water — bubbles mean a leak, no exceptions. Cycle the locker several times and watch how quickly it engages and how the tank pressure recovers.
If the tank drops below roughly 40 psi before the compressor cuts back in, the tank is undersized for the job or the compressor's duty cycle is too low. Adjust cut-in/cut-out settings until engagement is consistent every time.
8. Final check and road test
Drive the vehicle, cycle the locker on and off a handful of times, and confirm it engages the same way every time regardless of whether the vehicle has been idle for hours or driven for a while. Recheck fittings after the first few drives once everything has settled and vibrated a little.
“If the tank drops below 40 psi before the compressor cuts back in, the reservoir is too small for the job.”
Troubleshooting
- Locker is slow to engage — usually an undersized tank or a compressor with too low a duty cycle for repeated cycling. Step up tank size before replacing the compressor.
- Compressor runs almost continuously — check every fitting for leaks first; a cut-out set too close to cut-in is the second most common cause.
- Locker disengages over rough ground — a pinched or loose air line at a point of suspension movement. Recheck the routing from step 5.
- Tank won't hold pressure overnight — a faulty check valve at the compressor outlet or a loose fitting at the tank port. Isolate each joint with soapy water to find it.
- Compressor overheats on longer fills — poor mounting airflow or a compressor undersized for a dual-locker setup. Relocate for airflow before assuming the compressor is faulty.
Tools and resources
Beyond the compressor, tank and fittings covered above, keep a pressure gauge and multimeter on hand through the whole install — most locker complaints trace back to either a pressure setting or a wiring fault, and both are quick to check with the right tool. A dedicated pressure switch install, and correct 12V compressor wiring, both deserve their own attention rather than being an afterthought on locker day.
What to do next
Once the onboard air side is running reliably, the same tank and compressor can often support other onboard air tasks — tyre inflation, air lockers on a second axle, or load assist airbags — provided the tank and compressor are sized for the combined demand, not just the locker alone.
FAQ
What is an air locker and how does it work?
An air locker is a locking differential that engages using compressed air rather than mechanical linkage or electronics alone. Air pressure moves a piston inside the diff to lock both wheels on that axle together, and it needs a dedicated onboard air supply to work.
Do I need a dedicated onboard air system for one air locker?
Yes, a single air locker still needs its own compressor, tank and plumbing to build and hold pressure. A small compressor and a 2 gallon tank is usually enough for one locker circuit in 2026 vehicle setups.
What size air compressor do I need for an air locker?
A 12V compressor rated for continuous duty, such as a PX01-class unit, handles one locker circuit reliably. Dual-locker vehicles or combined tyre inflation and locker use need a higher duty-cycle compressor and a larger tank.
How big should the air tank be for a single air locker?
A 2 gallon aluminium tank is enough to buffer one locker's demand and reduce how often the compressor cycles. Step up to a 3 gallon or larger tank if the compressor also feeds tyre inflation or a second locker.
Can I run air suspension and an air locker off the same compressor?
It's possible if the compressor and tank are sized for the combined demand, but most setups run better with a tank large enough to serve both without either system starving the other under load.
Why is my air locker slow to engage?
A slow-engaging locker is almost always an undersized tank, a leak somewhere in the line, or wiring run through a weak accessory circuit. Check tank size and fitting integrity before assuming the locker itself is faulty.
How much psi does an air locker need?
Most air-operated lockers engage reliably in the 60 to 90 psi range, though the exact figure depends on the locker manufacturer's specification. Build the onboard air system to comfortably exceed the locker's minimum requirement.
Is it better to run a pressure switch or a digital controller?
A simple pressure switch is enough for a single locker circuit and is the lower-cost option. A digital controller adds visibility of tank pressure and easier adjustment, which is worth it once you're running more than one air-fed component.
One last thing
The wiring circuit trips up more installs than the plumbing does. A compressor wired through a thin accessory-circuit fuse will still build pressure — just slowly, and it'll get slower as the wiring corrodes over the next year or two. Running a dedicated relay and fused feed straight to the battery on day one saves a diagnosis headache down the track.
