Air Suspension Compressor Diagnosis & Replacement
(Classic, 4.0/4.6)


Introduction
Failure Modes & Diagnosis
Removal
Replacement with New or Used Genuine Compressor
Repair or Rebuilding of Genuine Compressor
Replacement with Thomas Pumps Model 315
Replacement with Generic Compressor


Photo: View of EAS compressor in place (4.0/4.6 model) with enclosure cover removed. Compressor for Classic EAS models (see picture below) is similar but with different mounts for underbody mounting.


Introduction
Note: Much of the information on this page and the Compressor Rebuild page was written before Range Rover owners had ready access to replacement parts and rebuild kits for their compressors from such suppliers as Rover Renovations. In those dark days when Land Rover monopolized the supply of air suspension parts,  several enterprising RR owners tracked down the information below on who made the OEM components and what their part numbers were, so later owners would not be held hostage by the genuine parts system. As a result, you can now get all the parts at low prices from aftermarket suppliers who used this information to obtain stocks of the necessary parts.

The RR air compressor has been criticized by some for being inadequate in capacity and too expensive, but in reality it is a sturdy industrial 1/5 horsepower 20 amp "Wobl" piston unit made by Thomas Pumps, one of the best-known manufacturers in the world. It is a member of the Thomas Pumps 315 model series (see details below), has a flow rate of about 0.96 cfm at low pressure, and according to justcompressor.com it can fill a 3 gallon tank from 0 to 150 psi in 4 minutes 45 seconds. It is commonly used by low rider fans to pump up their vehicles. It has to keep the 10 liter (2.5 gallon) Range Rover air tank charged up to 10 bar (150 psi), which is a much higher pressure than most off-road air compressers can reach. The compressor also has a much harder life than the average air compressor, having to operate in hot under-the-hood conditions (it is rated at 158 degrees ambient) for hundreds of hours rather than a few minutes at a time.

Normally, the compressor seems to wear out somewhere in the region of 120,000 to 150,000 miles (mine gave out at 140,000 miles). Replacement is an easy operation that requires no special tools. (Officially it requires the TestBook, or a Rovacom or Autologic equivalent, to depressurize the system before removing the compressor, but I bypass this step without problems. However, as always, use these shortcut procedures at your own risk!)

Failure Modes and Diagnosis
As the compressor nears the end of its natural life, it gets slower in its pumping (if it takes more than about 8 minutes to pump up, the EAS ECU will register a fault). Also as the pump ages, the bearings get worn and start making a clattering noise. When it gets to this stage it should be replaced as failure is imminent.

If the compressor runs constantly but the suspension does not pump up, the compressor is very far gone or more likely there is an air leak somewhere. Inspect all connections and air springs for leaks by listening for hising sounds or spraying on leak detector or soapy water. It is also possible that the diaphragm valve in the valve block is faulty and is letting air out as it comes in.

I recently had this symptom  recently had this constant pumping symptom and after I had dismantled everything in preparation for swapping out the valve block, the cause turned out to be a simple leak in the hose between the compressor and the valve block.  A section of the hose had been in contact with the EAS enclosure and the vibration of the compressor had caused the hose to be abraded away to such an extent that it wore right through.

If the compressor does not run when it should, possible causes include:
Failure of the pump motor
Blown fuse 44, Maxi Fuse 2, or Relay 20 (all in the engine compartment fuse box)
Faulty thermal cutout switch in the compressor
Faulty pressure switch in the EAS valve block
Faulty EAS ECU

The easiest way to diagnose the power flow is to unplug relay 20, connect its output socket to 12V and see if the pump runs. If so, the pump itself is obviously OK, and one of the other faults is present.

If voltage is getting to the compressor but it does not run, the problem could be the thermal cutout switch falsely telling the ECU that the pump is overheated. (The compressor is only rated for about 15% duty cycle at maximum pressure, hence the need for a thermal cutout). In my case, although the pumping was becoming slow and the bearings were getting noisy, the failure of the thermal cutout was the immediate cause of failure. This switch (the third and thinnest lead, colored orange, emerging from the pump motor body) is normally connected to the ground lead of the compressor; it open circuits when the operating temperature gets too high. On mine, the cutout switch open circuited for no particular reason, telling the ECU that the pump should be switched off. I was able to get the system going again by grounding this lead with a jumper.

If the pressure switch in the EAS valve block is faulty, it can tell the ECU that no pumping is needed when it is. To check this out, you can unplug multiplug C152 from the valve block drivers (see photo at top of page for its location) and test the resistance between terminals 7 and 9 on the valve block side of the plug; an open circuit should be noted if the sustem pressure is below 8.5 Bar (120 psi). Or, check pin 13 on the Air Suspension ECU under the left front seat -- if it shows +12 volts the pressure switch is closed, indicating that it thinks 150 psi has been reached.

For more exhaustive information on the air suspension system and its numerous failure modes, see the EAS Diagnosis and Field Repair page.

Removing the Compressor
On the 4.0/4.6, the EAS compressor, valve block and driver circuitry are located in a black plastic enclosure at the left rear corner of the engine bay, labeled "EAS". The top cover is removed by pressing on the two tabs on its front side. You can then tilt up the front of the cover and disengage the tabs at the rear. The photo at the top of this page shows the layout of the compressor and valve block with the cover removed.

On the Classic, the compressor, valve block and driver circuit, and the air dryer are all mounted together in an enclosure beside the chassis rail near the air tank. TO remove the compressor you first have to remove the enclosure as shown in teh photo above at left.

The offical shop manual dictates that the system should be depressurized using the Testbook before removing the compressor. I ignored this step; you may or may not wish to do so at your own risk!

Next, disconnect the 3-lead compressor connector (photo below). Then undo the 3 mounting nuts that secure the compressor, and lift it partly out of the enclosure. Further movement is constrained by the blue outlet hose on the compressor pump (see photo at top of page). Position the pump so you can access and undo the brass nut (12 mm wrench) on the pipe union for this outlet hose (photo below).  If  you did not depressurize the system and were lucky enough to have pressure in it before you started, and your valve block and the rest of the system is in good condition, only a short puff of air should escape. The pump can now be withdrawn completely.

Replacement with New or Used Genuine Compressor
Replacement is the reverse of removal. Be sure to tighten but not overtighten the nuts holding the compressor and anti-vibration mountings in place. Check the outlet pipe union for leaks (by ear or by spraying air leak detector fluid or soapy water on it).

The genuine compressor is still expensive at the time of writing (November 2003). The unit for the 4.0/4.6 costs about $440 at the dealer. Atlantic British has them for $389.95. The lowest price I have seen for new ones  lately is $375 (with free shipping) at SpeedyCarParts.com. More recently, I found that Airbag Man in Brisbane, Australia, sells them to export customers for A$400 or US$300 and ships inexpensively worldwide (prices to Australian customers will be higher due to local import duty and sales tax).

The compressors shown on this page are for the 4.0/4.6 models, but Jeff Wheeler reports the pump itself is the same on Classic EAS models -- all that is different is the mounting tabs which are attached to it to enable mounting in a box under the vehicle, as opposed to the under-hood position used on the 4.0/4.6. Jeff had to pay $512.95 for the Classsic pump (Atlantic British has them for $509.95). If this is the case, you could replace the pump on the Classic with the 4.0 pump, and re-use the mounting brackets off the old pump.

Used compressors are now readily available from wreckers (I got one from a 1999 Range Rover for $225) and come up periodically on eBay.

Repairing or Rebuilding the Genuine Compressor
(For full details see the  EAS Compressor Rebuild Page) and the Air Compressor Field Repair / Temporary Rebuild Page).

The genuine compressor appears to be made by Thomas Pumps, a highly regarded US brand. Because Thomas is a common brand of compressor, you can probably get the genuine one rebuilt by any rebuilder of air compressors. Abe Thietten of Austria took his geniuine compressor (which was still running, but without any pressure) apart and found that only the Teflon piston ring was worn out. Thomas pumps in Germany offered to repair it, with a minimum value for repair orders of €80 -- i.e. US$100. I recently discovered that Airbag Man sells a complete Thomas compressor service kit that includes new sleeve and inston/conrod assy, sells for A$200.00 or about US$150. They are located in Brisbane, Australia and ship worldwide. More recently (2006) a new source has been established in the US by fellow Range Rover enthusiast Dennis Altman. His Rover Renovations company sells completely rebuilt compressors for about $220 (Classic) and $240  (4.0/4.6), compressor rebuild kits, and numerous specific parts for the compressor including the seals, mounts and motor brushes.

For detailed information on the rebuild procedure, please see the EAS Compressor Rebuild Page.

A temporary "rebuild" can be achieved using home made parts; see the Air Compressor Field Repair / Temporary Rebuild Page.

Replacement with Thomas Pumps 315 model
Note: Update 2007: Brand new (and reconditioned) compressors can now be obtained from aftermarket sources such as Rover Renovations. The information below documents the pioneering work of early RR owners who tracked down the OEM manufacturers and parts now readily available from such suppliers.

From my researches of the Thomas pumps catalogs, the closest Thomas model number appears to be the 315CDC5612 -- specs are available on the Thomas Pumps website at this link. A Rangerovers.net forum member has talked with people at Thomas Pumps who confirm that the OEM unit is in fact a Thomas 315 model -- the only modification made for the Land Rover unit was the location of the air filter. Land rover needed to mount it upside down so they could fit the plastic cover over the EAS components and still be able to close the hood. Other than that the Thomas 315 will bolt right in. Of course, you will have to splice te leads into the Land Rover electrical connector.

Abe Thietten found a Thomas 315 series compressor at Puma Sales  for $109, but it is unclear whether the one he got is the exact replacement as I found at least 7 identical-looking models in the 315 range with different specs. Unfortunately, only the 315CDC5612 is rated at the necessary 150 PSI, while the "standard" 315 model has a shorter stroke and is only rated at 130. I did find what appears to be the right model at a vendor on eBay who uses four of them in his low rider rig. He has a large stock of them and sells them new for $139. To find them, search eBay for Thomas compressor. Jeffrey Wheeler found this model at a local Thomas pumps distributor for $185.

Christian Springer reports from Austria that he swapped in a 315CDC5612 (purchased on eBay for $100) on his 1996 Range Rover 2,5 DT automatic. He reports: "It fits and works perfectly; assembly is simple because you can use the old mounting brackets, although there are some little differences to the OEM compressor: The 315 is 9 mm (1/3 inch) shorter then the OEM. If you mount the rear bracket to the pump body with longer screws and washers or a nut (see photos below) you can adjust the length exactly. I used the original screws and extended the length by 5 mm which is enough to place the compressor easily and without tension into its position.

"Position and thread of the air intake is different from stock. The air intake is located opposite to the exhaust, but with the filter in this position the 315 doesn’t fit into the EAS box. It makes no sense to leave the filter in the front bracket like it was on the OEM, because no air is coming in there on the 315. The cylinder head of the OEM has two holes to get air from the crank case, the 315 hasn’t. Either you change the cylinder head also, or you drill wholes into the 315’s cylinder head or you change the filter position. I selected the latter, since I did not want to open the new 315. There are various 1/8" NPT angle adapters and hoses, I used a 3/8” brass flexible hose which I had on stock (see photo below right), shortened both ends, plugged the filter into the flexible end and cut a thread onto the other end. Because I have no 1/8" NPT thread cutter I’ve cut a M10 thread. With some Teflon tape around it I had no problem to screw it tight.

"The orange lead which was connected to the OEM compressor's thermal cut-out switch has to be connected to ground. According to data sheet the 315 is also thermally protected, but controlled internally and not from outside like the OEM. So it has only the two wires for current supply. I left the old connector plug on the (repairable?) OEM compressor and pressed casual car-electric flat plugs onto the ends of the 315’s wires which fit perfectly into the car’s connector socket.

"I haven’t opened the 315, but the motor seems to be a little bit different to the OEM’s one. As mentioned it’s shorter and therefore the 315's weight is almost a half pound less compared to the OEM. The 315 series datasheet contains a hint that a heavy duty motor (Model 305) is available for custom applications. This might be the motor used in the OEM compressor. Maybe the 317 series is also a good alternative one. More expensive, but also more heavy duty. The datasheet shows that the 317CDC56/12 has exactly the same length like the OEM compressor but a higher diameter of the motor (81 vs. 65 mm) and 1/4” instead of 1/8” NPT intake and exhaust. The positions of the bracket screws seem to be the same on all models. If my Rangie’s life should exceed that of the 315 compressor I’ll try a 317 next time and tell you ;-)."


Replacement with Generic Compressor

Blowjax:
Abe Thietten replaced his OEM compressor with a cheaper but more powerful Blowjax pump that he found at Puma Sales for US$99. This is a 1/4 horsepower compressor (the OEM unit is 1/5 horsepower) called the  Blowjax DC2000. Abe kindly provided the photos and installation details below.

Abe reports it fits perfectly (see photos above and below). You can line up the bracket on old air compressor with the new one and drill two holes to attach it (see photo below at left). Because of this compressor's slightly larger size, the lid to the EAS system will only attach on the front,  not on the back. (Adam feels it would close here too if you modified the brackets to lower the compressor a bit). For the air line, the old adapter screws directly into the new Blojax air compressor's 1/8" NPT outlet port, but before you do this you will have to rotate the top cylinder head so it points backwards. This pump comes with a filter and it is located on the side (see photo below right); it fits into the enclosure with no modification. However you will also need to re-wire the electrical connections using your old connector.

The Blowjax pump is a heavier unit than the original pump, with large cooling fins on the pump body. According to this link on the justcompressors.com site, this compressor (also known as the DC02) can fill a 3 gallon tank to 150psi in 6.7 minutes, actually slower than the OEM pump if these figures are accurate, but has higher flow rates at low pressure (1.23 vs 0.96 cfm at 0 psi) and is rated for a 33% to 50% duty cycle as opposed to the 15% of the OEM part. Thus it is a particularly good choice if you have tapped into the EAS system like I did to pump up tires. It does not  have thermal cutout protection, so you need to ground the thermal sensor wire going to the compressor connector to fool the Range Rover suspension ECU into thinking the non-existent thermal switch is working. As a result, there is a possibility this pump could overheat, so use at your own risk (however Abe reports that in practice it runs very cool). Joe Marotta tried the Blowjax installation and has the following advice on the overheating problem: "The breaker that comes with the kit can at times trip if it gets too hot, so by running it through to the inside of the truck, it will save you many headaches when the breaker goes off, and you don't notice it untill you get EAS fault because there isn't enough pressure. By running it inside, I have not had a problem since."

Viair, AIM:
Other readers have tried various replacement compressors of the type normally used in low rider suspensions, made by Viair and AIM. The main thing to watch out for with these compressors is excess noise and vibration -- the OEM Thomas unit is exceptionally smooth running compared to most. Some owner experiences, good and bad, are detailed below.

One owner tried an AIM compressor and reports: "Though it works fine, it vibrates like... If you use your RR mainly on the road and want it to remain a luxury 4x4, go with the OEM compressor - a repair kit is available from airbagman for about $150". (For more details see the compressor rebuild page). He thinks that next time he would upgrade to a 317, which can be mounted in the OEM location and function just like an OEM compressor.

Another reader reports " I replaced mine with a VIAIR 325-30. First I mounted it inside the valveblock over the wheel but the vibration and noise was unacceptable. I then mounted it on the chassis behind the front bumper ... tight fit ... a real pain to fit. This was better but still too noisy for me. I ended up getting an OEM."

One 1995 4.0 owner used the Viair 350. He reports "It moves about 1.4cfm compared to the oem’s .4cfm and has a 100% duty cycle compared the 25% for the oem. This means it will move a lot more air a lot faster. My truck will now go from access height to standard height in about 4 second and the day I timed it the temp. was about –20. Aim also make a very good compressor. I can not remember model numbers off the top of my head but I know they make on that will bolt in easily. Got got my Viair 350 from ckcustoms.com They offer a lot of different compressor and were great to work with."

Another reader suggests the Viair 380: "It's got a great duty cycle (especially compared to the OEM Rover compressor) and will fill the tank fast. Looking around, it can be had for less than $200, so it beats a new Rover pump in price, as well. Since it's a large unit, however, some "creative" mounting will be required. I'll either mount it on the passenger side of the engine bay (loads of room there) or under the vehicle, near the tank (not sure of all the ramifications in doing this yet)."



More Information
Air Compressor Field Repair / Temporary Rebuild Page
Air Compressor Rebuild Page (official rebuild procedures)
Air Suspension Information, Diagnosis and Field Repair page.
Airbag Man Compressors & rebuild kits
Range Rover Parts Sources page under "suspension"
Rover Renovations Low cost EAS parts, rebuild kits, new and rebuilt compressors