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Cut the blue... No, the red.... No, errr im colour blind... We are all going to die
P38A 2.5dt FIP static timing & ominous HotStart found
- Thread starter RangeRoller dt
- Start date
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RangeRoller dt
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Colour blind? Don’t worry yours is a nice shade of purple
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It's actually yellow!Colour blind? Don’t worry yours is a nice shade of purple
RangeRoller dt
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So the HotStart works, I know this because without it my P38 doesn’t
The glows (now has new glow in cyl1) come on every turn of the ignition for 6seconds like a timer and comes on dash then goes out.
Without it no glows and very very hard to start even with a 100% 1000cca battery and decent OE starter motor!
@wammers there are two blue wires with a transistor across the pins to them, pins 30 & 87a, these are spliced into a gray/blue trace wire on ecu
Pin 87 is blanked
Pin 85 is the black cable that runs to a small earth below the fusebox
Pin 86 is the red that leads up the wing and through the bulkhead. It goes down through the inertia switch - panel to which I probably can’t get off without breaking it so left alone. My guess is it either goes to becm under seat or the tank pump??
The glows (now has new glow in cyl1) come on every turn of the ignition for 6seconds like a timer and comes on dash then goes out.
Without it no glows and very very hard to start even with a 100% 1000cca battery and decent OE starter motor!
@wammers there are two blue wires with a transistor across the pins to them, pins 30 & 87a, these are spliced into a gray/blue trace wire on ecu
Pin 87 is blanked
Pin 85 is the black cable that runs to a small earth below the fusebox
Pin 86 is the red that leads up the wing and through the bulkhead. It goes down through the inertia switch - panel to which I probably can’t get off without breaking it so left alone. My guess is it either goes to becm under seat or the tank pump??
RangeRoller dt
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There are three other non standard wires that go through with the red wire above. Two are white for the dash switch that isn’t connected to anything - my guess is the hotstart originally had an on/off switch or there were spotlights or something
The other is a red/yellow trace that goes from the fusebox relay connection in the corner to the hevac area??
The other is a red/yellow trace that goes from the fusebox relay connection in the corner to the hevac area??
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Someone's had a tinker then!
RangeRoller dt
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They knew what they were doing on some level - it won’t work with it disconnected
I have receipts for this work (past vehicle history) from LR themselves!
I have receipts for this work (past vehicle history) from LR themselves!
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- 19,277
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- Buckinghamshire, UK. ('95 DT)
They knew what they were doing on some level - it won’t work with it disconnected
I have receipts for this work (past vehicle history) from LR themselves!
I wonder if someone retro fitted a later HEVAC and had to put a relay to pull the clutch in? Think it was that. There was something different that required more current anyway. @martyuk would remember.
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You don't need a relay to pull the clutch.
Datatek
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I thought the relay was necessary for the later HEVAC as the drive transistor is not up to the job?
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Latest Hevac replaces all previous versions. Relay 3 was only fitted to MY 1999 and on. Mine does not have relay 3 but is fitted with latest unit and has worked fine for the last eight years. There once was a retro fit kit to incorporate relay 3, can no longer be obtained and was typical Land rover ridiculous money. There is however no problem rigging up relay 3 if the owner has the nous, a relay and a bit of wire is all that is needed. Hevac pulls relay and relay supplies power for clutch from a fused source. Pretty simple mod. But as said mine works fine without relay 3.
Datatek
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In that case, I wonder why LR went to the trouble of fitting a relay? They are not known for spending money unnecessarily. Do you use your aircon much?
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It is used as needed.
Datatek
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So not very often in the UK then
Maybe under constant use the HEVAC output is not up to the job.
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So not very often in the UK then
Maybe under constant use a relay would be a better option. Maybe the relay was added for countries where constant use is required, but is not needed in cooler climates, but fitted across the board for ease. Earlier fuse boxes have the relay 3 position. As said, easy to retrofit for you and i, not so easy for most on here.
martyuk
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I believe it was originally mostly for GEMS petrol vehicles - the compressor clutch plate was known for wearing, and you could remove shim washers to close the gap and get it back within spec. The HEVAC controller drives the compressor clutch through a MOSFET (same as for the lights etc) and it has a status feedback on it to detect things like short circuit, under load, over load etc. Earlier HEVAC controllers used this to throw an fault code if it thought there was an issue with the compressor clutch, but it also meant that when the clutch wore, it wouldn't pull in properly, or show a lower load to the HEVAC, which would then throw the fault and stop trying to drive the AC compressor. Also if the level of refrigerant dropped so the trinary switch didn't pull it, and thus no compressor clutch, it would flag as a compressor clutch fault.
The additional relay wiring harness was to provide a direct feed from battery voltage (rather than thru HEVAC, Circuitry, and all that) which had enough of an jolt to pull the compressor clutch in. There was something like a 4 ohm power resistor on the control wire from the HEVAC to present a constant load to it, which kept it happy, and then the clutch get full battery voltage now through the switched relay.
Later GEMS vehicles had the wiring and fusebox changed (one of the reasons for there being 2 different GEMS fuse box part numbers I imagine) and then the later HEVAC controllers had a firmware update to ignore the status wire on the compressor clutch MOSFET (as it will still operate - like BECM ones do if you put LEDs in for example, without a load resistor - the light will still illuminate, but you get the error message on the dash). So with that ignored, you don't need the power resistor to present a load.
I guess they just carried it on for the later Thor models, and probably later diesel models. The later (JFC part numbered HEVACs) will drive the compressor clutch directly on the older vehicles, with no error message as it's still the same MOSFET on the output. But earlier AWR1012/5051 etc HEVAC controllers won't work properly with the later vehicles, as whilst the MOSFET will drive the relay no problem, the status pin will still flag an under-load situation, which the HEVAC on earlier firmware sees as a compressor clutch fault and shuts off the output.
Datatek
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Thanks for a proper explanation.
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That makes sense for me as my HEVAC threw a compressor clutch failure when the refrigerant dropped! Mine's a '95 as is RRDT.
I wonder if RRDT has a HEVAC retrofitted from one of the intermediate units and then someone wired in a relay to overcome the fault? Hard to say without him tracing the wires, I guess.
RangeRoller dt
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Trace the wire to exactly where it goes? Doubt it’s the radio connected to the ac relay.
Don’t know what model hevac it is or if ac clutch works. It seems to cool but rely on ram air, if you stop in traffic it goes warmish. Don’t really use it as lowering the window is much cooler
Don’t know what model hevac it is or if ac clutch works. It seems to cool but rely on ram air, if you stop in traffic it goes warmish. Don’t really use it as lowering the window is much cooler
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- Buckinghamshire, UK. ('95 DT)
My AC is excellent. Better than my mother's Fiesta and that's nearly 20 years younger.
