P38 Paul Posted August 21, 2023 Share Posted August 21, 2023 Hi all, I have a EAS compressor that doesn't run unless I bridge the relay terminals, where do I start looking for the fault to get it working as it should? Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted August 21, 2023 Share Posted August 21, 2023 That sounds like the relay isn't being triggered or the relay is faulty - if the compressor runs it's presumably not faulty Quote Link to comment Share on other sites More sharing options...
elbekko Posted August 21, 2023 Share Posted August 21, 2023 Could be the thermal switch inside? Quote Link to comment Share on other sites More sharing options...
geoffbeaumont Posted August 21, 2023 Share Posted August 21, 2023 Bridging the relay shouldn't work if it's the thermal switch? The problem has to be external to the pump itself. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted August 21, 2023 Share Posted August 21, 2023 19 minutes ago, geoffbeaumont said: Bridging the relay shouldn't work if it's the thermal switch? The problem has to be external to the pump itself. From that diagram it looks like the pump overheat switch signals the ECU so bridging the relay out would bypass that and force the motor to run. If it's just the temp switch that is likely an easy fix too. Quote Link to comment Share on other sites More sharing options...
elbekko Posted August 21, 2023 Share Posted August 21, 2023 1 hour ago, FridgeFreezer said: From that diagram it looks like the pump overheat switch signals the ECU so bridging the relay out would bypass that and force the motor to run. If it's just the temp switch that is likely an easy fix too. Precisely. The temp switch is inside the pump, though. But I do believe it can be fixed. Or bridged... Quote Link to comment Share on other sites More sharing options...
geoffbeaumont Posted August 21, 2023 Share Posted August 21, 2023 1 hour ago, FridgeFreezer said: From that diagram it looks like the pump overheat switch signals the ECU so bridging the relay out would bypass that and force the motor to run. If it's just the temp switch that is likely an easy fix too. Ah...helps when I'm not on a phone and can see the diagram properly... Quote Link to comment Share on other sites More sharing options...
P38 Paul Posted August 22, 2023 Author Share Posted August 22, 2023 On 8/21/2023 at 10:22 AM, P38 Paul said: Hi all, I have a EAS compressor that doesn't run unless I bridge the relay terminals, where do I start looking for the fault to get it working as it should? A quick update, I bridged the compressor last night & when it started lifting I swapped the bridge wire for the relay & it kept running to full pressure then cut out as it should, went to the car this morning & its not working again. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted August 22, 2023 Share Posted August 22, 2023 Have you tested any of the connections shown in the circuit diagram - is the relay coil being fed 12v from the ECU (C176-1), is the overheat switch grounded or open circuit (C151-2), does it work if you put a different relay in? I'm not familiar with the whole system / circuit so worth a read of the RAVE manual to understand how it works - I assume there's a pressure switch in there too. Quote Link to comment Share on other sites More sharing options...
P38 Paul Posted August 22, 2023 Author Share Posted August 22, 2023 2 hours ago, FridgeFreezer said: Have you tested any of the connections shown in the circuit diagram - is the relay coil being fed 12v from the ECU (C176-1), is the overheat switch grounded or open circuit (C151-2), does it work if you put a different relay in? I'm not familiar with the whole system / circuit so worth a read of the RAVE manual to understand how it works - I assume there's a pressure switch in there too. Hi Fridge, you are talking to a complete idiot here, the only thing I can say at the moment is that I have tried multiple relays so I think I can rule the relay out. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted August 23, 2023 Share Posted August 23, 2023 OK so looking at the diagram; The relay has a green wire to activate it from the ECU so that should get 12v when the ECU wants to switch the compressor on. The black wire (coil ground) should be a good earth (~zero ohms resistance from that wire to ground). The black/purple wire from the compressor is for the overheat switch, it looks like that should normally be grounded (~zero ohms resistance from that wire to ground). There's also the wires for the pressure switch inside the valve block and what looks like a shutoff timer or relay and an "air suspension inhibit switch" X209 - Electrical troubleshooting manual is here - Page 308 on is the EAS system including full circuit diagrams. Quote Link to comment Share on other sites More sharing options...
Escape Posted August 23, 2023 Share Posted August 23, 2023 As above, most likely suspect is the thermal switch in the compressor. The thin black/purple wire on the compressor connector should have continuity to the ground (i.e. the thick black wire in the same connector). If it doesn't, the switch has failed. They can be replaced (new ones are available to solder in) or bridged. Simply ground the BP wire and see if the compressor runs as a first test. It's unlikely to be the ECU, unless there is a fault, which should be indicated on the dash. Pressure switches are often replaced, but rarely the cause. 1 Quote Link to comment Share on other sites More sharing options...
P38 Paul Posted September 7, 2023 Author Share Posted September 7, 2023 I have just tried two more compressors & none of them are working until the relay is bridged, one of the compressors was removed from my car working two years ago just needing a new piston ring so I think that rules out a compressors being at fault. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted September 7, 2023 Share Posted September 7, 2023 1 hour ago, P38 Paul said: none of them are working until the relay is bridged Still sounds like the relay or what triggers the relay then. Back to the question from a few posts up - do you see volts across the relay coil terminals when you're expecting it should be triggered? Quote Link to comment Share on other sites More sharing options...
P38 Paul Posted September 9, 2023 Author Share Posted September 9, 2023 On 9/7/2023 at 4:55 PM, FridgeFreezer said: Still sounds like the relay or what triggers the relay then. Back to the question from a few posts up - do you see volts across the relay coil terminals when you're expecting it should be triggered? Hi Fridge, the compressor is intermittent, when it doesn't run there is no voltage across the relay coil terminals, when it decides to run I have got 14v across the coil, its got to be whatever triggers the relay that is at fault but what am I looking for or where am I supposed to be looking? PS, The black/purple wire from the compressor is grounded all of the time. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted September 9, 2023 Share Posted September 9, 2023 I don't know about the rest of the system and how it decides to cut the compressor in or out - there must be a pressure switch somewhere at least. There's a few of these which may be of use: https://fuddymuckers.co.uk/rtfm/RangeRover/P38/RR_P38_Electrical_Troubleshooting_1995.pdf https://fuddymuckers.co.uk/rtfm/RangeRover/P38/RR_P38_Electrical_Troubleshooting_1996.pdf https://fuddymuckers.co.uk/rtfm/RangeRover/P38/RR_P38_Electrical_Troubleshooting_1997_1999.pdf https://fuddymuckers.co.uk/rtfm/RangeRover/P38/RR_P38_MY95_Electrical_Troubleshooting_Manual_LRL0006ENG_4th_Edition.pdf https://fuddymuckers.co.uk/rtfm/RangeRover/P38/RR_P38_MY99_On_Electrical_Troubleshooting_Manual_LRL0329ENG_5th_Edition.pdf Not sure how much difference the years make. Workshop manuals: https://fuddymuckers.co.uk/rtfm/RangeRover/P38/RR_P38_WSM_1995.pdf https://fuddymuckers.co.uk/rtfm/RangeRover/P38/RR_P38_WSM_1995_UK.pdf https://fuddymuckers.co.uk/rtfm/RangeRover/P38/RR_P38_WSM_1995-1999.pdf Quote Link to comment Share on other sites More sharing options...
elbekko Posted September 9, 2023 Share Posted September 9, 2023 Indeed probably the ECU deciding to not run the compressor, then. Do you have an EAS cable to connect a computer to the car? Quote Link to comment Share on other sites More sharing options...
P38 Paul Posted September 9, 2023 Author Share Posted September 9, 2023 23 minutes ago, elbekko said: Indeed probably the ECU deciding to not run the compressor, then. Do you have an EAS cable to connect a computer to the car? Yes, I have the cable that connects to the Nanocom. Quote Link to comment Share on other sites More sharing options...
Escape Posted September 9, 2023 Share Posted September 9, 2023 You seem to have ruled out the compressor. The ECU's rarely fail, I've only seen one in 15 years or so, but it can happen. It could be something simple as a bad connection in the wiring. Not always easy to find, unfortunately. The wire triggering the compressor relay is a green one, straight from the ECU (pin 8 ) to the relay. Quote Link to comment Share on other sites More sharing options...
elbekko Posted September 10, 2023 Share Posted September 10, 2023 19 hours ago, P38 Paul said: Yes, I have the cable that connects to the Nanocom. Any faults logged? If it's refusing to start the compressor for a reason, that reason should result in a fault. Quote Link to comment Share on other sites More sharing options...
P38 Paul Posted September 10, 2023 Author Share Posted September 10, 2023 51 minutes ago, elbekko said: Any faults logged? If it's refusing to start the compressor for a reason, that reason should result in a fault. There are a few faults logged on the Nanocom which I presume are from the none triggering compressor, they all come up as "invalid fault code". Quote Link to comment Share on other sites More sharing options...
P38 Paul Posted September 10, 2023 Author Share Posted September 10, 2023 13 hours ago, Escape said: You seem to have ruled out the compressor. The ECU's rarely fail, I've only seen one in 15 years or so, but it can happen. It could be something simple as a bad connection in the wiring. Not always easy to find, unfortunately. The wire triggering the compressor relay is a green one, straight from the ECU (pin 8 ) to the relay. Hi Filip, I replaced the ECU in March this year under the the post OBD socket, no power. By P38 Paul, March 8 . Surely it cant be that again could it? Quote Link to comment Share on other sites More sharing options...
Escape Posted September 10, 2023 Share Posted September 10, 2023 Right, I remember that topic, just not that it was you... All the more reason to have a good look at the wiring. A short in the wrong place can damage an ECU. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.