Discovery 3 Air Suspension Compressor
Air Compressor Assemblies
There are three different designs of compressor assembly, Hitachi, early type AMK and late type AMK, of which only the AMK units (early and late, successively) were available for some years. Originally Land Rover Discovery 3's were fitted with the Hitachi unit.
If at some point in its history, your Discovery 3 has required a new compressor, it may have been fitted with the early type AMK unit or (possible, but unlikely) the late type AMK unit because of non-availability of the original Hitachi unit. This will have involved some modifications to the vehicle.
More recently, a Hitachi-type compressor has been reintroduced to the market, manufactured by Dunlop. This has once again made possible the like-for like replacement of an air compressor, so long as the old unit on your vehicle is of the Hitachi type and the vehicle has not been modified to accept an AMK unit.
To order a compressor or replacement parts, you must first identify the type of compressor on your car. The most recognisable features of the Hitachi unit are a hexagonal end cover on the air dryer mounted alongside the compressor and a 'D' shaped cradle holding the whole assembly to the car through upper and lower rubber mountings.
AMK compressors have a round end cover on the dryer and mount to the car by a large plate angle bracket. The visual difference between early and late AMK compressors is subtle: the early type features an upward-angled air inlet tube with push-fit hose connection, while the later type has a horizontal screw union to the inlet hose.
If the air compressor assembly requires replacement:
Because of the reintroduction of the Hitachi type unit (now manufactured by Dunlop), a like-for-like replacement with no required vehicle modifications can be made if the old unit on your car is still of the Hitachi type.
If however your vehicle has at some point in its life been modified to take an AMK compressor, then you should fit an AMK type compressor as a replacement: re-engineering and re-programming your car back to accept an Hitachi type compressor would be time-consuming and expensive.
The official Land Rover policy on compressor replacement is still to modify the vehicle to accept a later AMK compressor. If you decide to follow this route, some adaptation or replacement of hoses will be required if an Hitachi or early type AMK compressor is replaced. Additionally the compressor relay will require replacement with a YWB500220 relay and, then replacing an Hitachi unit, the upper and lower compressor covers will need to be changed for the AMK type as well, Finally, the electronic control unit for the air suspension will require installation of new software via the vehicle's diagnostic system.
Full details of the conversion work required to fit a late type AMK compressor to a Land Rover Discovery 3 are given in Land Rover Technical Bulletin LTB00420, available on request from Rimmer Bros.