Install an on-board Air Compressor


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A useful addition to all Land Rover models : credit: © Alisdair Cusick
An on-board air compressor can be fitted to most Land Rovers. Alisdair Cuisick finds what’s involved in fitting one to a Defender 110

Need to know

Time: 3 hours.
Difficulty: 3 out of 5 stars
Models: All Land Rover models.
Tools needed: Metric and imperial spanners, crimping tool, heat gun, wire strippers, insulating tape, drill, PTFE tape.
Parts used: DA4985 twin on-board compressor £345; DA6837 manifold kit £51.49; 3501010 mounting kit £118.40; 7450107 pressure control kit £203.39.
Work safely:
Always wear gloves when handling or manipulating corroded metal.
• Use the right tool, for the right job.
• Be fire safe in the workshop if cutting or grinding.
• Understand wiring fully before powering up an electronic system – if in doubt, confirm correct operation with a multi-meter.
• Get an expert to do the job, if in any doubt.
• Compressed air can be lethal: never horseplay with an air supply.
Thanks to: Steve Grant and Britpart for help with this feature.


Besides inflating tyres and accurately deflating them for soft ground, or running air locking diffs or powering tools, compressors can also be useful for lifestyle hobbies, such as camping or using inflatable paddle boards. Editor Patrick found a need for a convenient and independent air supply when out with his Defender, and the answer was an on-board air compressor. We show how to fit one to his 1998 Defender 110.

Depending on intended use, you may find a smaller model of compressor more convenient, say, if you’re just needing the air supply to run diff lockers. Models matched to that supply requirement are more compact, and can be mounted in smaller locations, even under the bonnet. So take time to choose, and speak to an informed retailer for advice, balancing what you need now, with some spare capacity, and allowing for an installation that suits you.



Lay it out and look: From left to right: mounting bracket, compressor, manifold and connector pipe, pressure regulator, outlet and pipework, supply pipe (plus two base plates not shown here).

Where is best? After discussion with Britpart’s Steve Grant, Pat decides to opt for fitting the unit behind the front passenger seat. Steve removes the nearside middle row seat, for access

Assembly begins: Working on the bench with everything ready, Steve begins assembling parts onto the mounting plate. The plate allows various set ups.

Valve block: Steve fits the valve block for the pressure regulator to the compressor manifold. PTFE tape is used on the threads to ensure an airtight seal.

Best layout: With compressor loosely test-fitted to check clearance and pipework routing, a suitable orientation for the manifold is chosen, before bolting it onto the compressor bracket.

Test fit, check: After test fitting the manifold connector pipe, then trial fitting the unit in the vehicle to check clearances, the compressor is bolted into the mounting bracket.

Top tip: The correct way to use PTFE tape is to wrap it the way the fixing tightens – so the tail end follows behind as the fitting is screwed in.

Here’s why: Wrapped this way, it threads easily, and flattens as you tighten, rather than clogging the threads. We use it on the supply fixings for the manifold, as here.

Axle feed: If you were running additional air lockers, this is the feed used for that air supply. Not needed in our case, but it’s there if Pat should decide.

Base plates on: On go the two base plates. These provide useful additional clearance, as well as allowing ventilation for the cooling fans underneath the compressor.

Piped air: On goes the connector pipe between compressor and manifold. Pipe fittings may not be metric. Make sure you use a well fitting spanner of the correct size.

Pressure kit: The pressure sensor valve and outlet connector are now fitted. No need for PTFE tape on these two, as they both incorporate a rubber O-seal for a  good seal.

Outlet hose: Steve fits the outlet hose. Our pipe is longer than needed, so Steve has laid out the components to allow for this. Ideally, the pipe would be shorter.

Wiring: The pressure sensor loom is connected up. The valve block connectors incorporate small Allen head bolts, to prevent them vibrating off in use. Don’t miss those out.

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Brain box: The pressure controller is fixed to the outside of the mounting plate using double sided tape. It is worth making a note of the bluetooth ID for reference.

Tidy up: Excess cabling is tidied up by fitting it to the back of the bracket with a P-clip. This faces to the rear, where the cabling can’t get snagged.

Colour connections: So wiring can pass through a bulkhead, the compressor loom connector need to be coupled up. Follow the wiring diagram carefully to ensure it is wired correctly.

Repeat the job: Do the same for the switch connectors after threading it though the aperture on the mounting frame. Double check you’ve got the wiring correct, then fit the switch.

Tidy job: Again, we have excess wiring for our application. You could shorten the loom, but Steve ties it up tidily and securely on the rear of the unit.

Power feed: The power supply for the pressure control module piggybacks the switch control feed wire. Steve wraps insulating cloth tape over the pair for a neat job.

Voila! That is the finished compressor assembly ready for the car. Our vehicle installation will allow for easy access in use, but keeps vulnerable parts out of the way.

Measure twice... Steve trial fits the whole assembly, then checks and measures before drilling the floor for the mounting holes, avoiding major body structures and wiring.

Bolt it up: The compressor is bolted in position. Use one bolt for the earth supplies, seen here. The battery loom is also fed under the front passenger seat in readiness.

Earth check: Having fitted the compressor and earths, check continuity with a multimeter between earth feed and the body; here, a rear door body rivet suffices.

Power supply: Steve finds an existing route for the power loom rather than drilling the seat box. Then he crimps on terminals, and fits heat shrink over those joints.

Vital feature: Connect up the loom at the compressor end. Steve fits a fuse link and connects up the battery. You may prefer an ignition feed for your application.

Neat job: The cables were routed through an existing cut-out in the seat base. Steve fits insulation to the edges of the cut-out, to avoid vibration damage to the cable.

Digital network: Power up the compressor, download the app, and pair the two via Bluetooth. There will be various preferences to set, including allowing igniton-on only operation.

Test: With the outlet hose connected, the pressure value pre-set, the app does the rest. The compressor thrums into life, inflating – or deflating – to the set pressure.


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