Replacing HVAC controller
- Thread starter Henrik97
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- Preston Lancs.
Plug and play. Don't switch ignition on until all cables are in place.
Datatek
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- Near Poitiers SW France
Is it the correct one?
Hi,
Well, it's the one I was advised to buy, since there was an inherent firmware fault in the earlier units. So the one I've bought is a JFC102550, whereas the old one is a JFC102400.
Still plug and play?
H
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- 58,170
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- Preston Lancs.
Yes. JFC102550 or JFC102540 (none heated seats) are the only ones available that can be purchased new. They supersede all other units.
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Datatek
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The early ones didn't use a relay for the aircon compressor, later ones do, depending on the year of your car, you may need a mod.
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- Preston Lancs.
Mine has the latest one fitted no relay and works without issue.
Datatek
Well-Known Member
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But for others it has not.
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- 58,170
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- Preston Lancs.
Maybe a lot of talk about it in various places but mine works. That is all i can say.
Thanks both of you. I suppose I'll just have to try it and see if it works or not. Is the required mod described anywhere, in case I need it?
Can you tell me how to access the screws in the fascia without damaging anything?
Thanks,
Henrik
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There is something about using post 98 HEVAC with pre 98 cars and vice versa here…
Range Rover P38 Maintenance repair improvements and tips learned by experience by ownership.
Under the MORE ABOUT THE HEVAC SYSTEM heading….
There is something about adding RL-3 to the fusebox and doing the 12v direct feed to the compressor clutch using the new loom part YMQ104590AA if you want to use the later type HEVAC panel.
The YMQ10590AA mod is to supply 12v direct to the compressor clutch, because the earlier design had to high volts drop in the circuit so the clutch in some cases didn't work. There is a bulletin about it in RAVE somewhere...
I should add, I'm not sure if this is the problem you might have, or whether it'll work, but it might help if you do have problems with your new unit…..
Range Rover P38 Maintenance repair improvements and tips learned by experience by ownership.
Under the MORE ABOUT THE HEVAC SYSTEM heading….
There is something about adding RL-3 to the fusebox and doing the 12v direct feed to the compressor clutch using the new loom part YMQ104590AA if you want to use the later type HEVAC panel.
The YMQ10590AA mod is to supply 12v direct to the compressor clutch, because the earlier design had to high volts drop in the circuit so the clutch in some cases didn't work. There is a bulletin about it in RAVE somewhere...
I should add, I'm not sure if this is the problem you might have, or whether it'll work, but it might help if you do have problems with your new unit…..
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tomcat59alan
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Interesting reading, will have to check on Rave the location of the "kernel of the poodle"
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- 58,170
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- Preston Lancs.
Thanks!
OK. The wiring loom seems pricey. Is there any reason why I couldn't just bodge it by using the existing feed to the compressor to fire a relay and then run a dedicated supply and fuse through the relay and to the clutch, with a resistor across the coil if it doesn't work directly? (Rather like the typical mod to make your high beams brighter on cars with flimsy wiring).
It seems risky to try and make it work without a control relay, as it would seem the later controller isn't built to handle the current draw of the clutch. However, if it can't handle the current of the clutch, I can't see why it would be better equipped to handle a similar draw through a resistor... If I don't have a relay RL3 in my fuse box already, I don't suppose the fuse box is wired for a relay in this position anyway, which probably explains why the OEM wiring loom is available from Rimmers.
Can anyone enlighten me on how to get the panel out of the dash?
Thanks for all your help lads!
Henrik
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- 58,170
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- Preston Lancs.
Undo the two centre consul side trims and slide them back. To reveal four screws holding Hevac unit in place.
Datatek
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The early HEVAC operated the compressor direct and used current sensing to detect operation of the clutch, it will not work with a relay as it doesn't draw enough current.
The later HEVAC operates the clutch via a relay, the drive circuit is not powerful enough to operate the clutch direct.
So there you have the reasons for the problems.
If you have an early car and you fit a late HEVAC, you need to intercept the line from HEVAC to the clutch and connect it to a relay and the relay contacts to the clutch. No need for fancy looms.
The later HEVAC operates the clutch via a relay, the drive circuit is not powerful enough to operate the clutch direct.
So there you have the reasons for the problems.
If you have an early car and you fit a late HEVAC, you need to intercept the line from HEVAC to the clutch and connect it to a relay and the relay contacts to the clutch. No need for fancy looms.
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There is also a resistor to put in too? I suppose this duplicates the coil resistance of the clutch to make the HEVAC think it's operating the coil directly instead of just the relay?
Not sure what the value of the resistor is though...
Not sure what the value of the resistor is though...
Datatek
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Resistor is required when fitting an early HEVAC to a late car, easier in that case to just remove the relay and add a jumper wire.
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Datatek
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There is a circuit diagram in the official loom installation instructions in RAVE.
Maybe that will help you knock something up.
Suitably over complicated.
Need more facts, does the car have a relay fitted for the compressor clutch? Is the replacement HEVAC the late version that requires a relay?
