HEVAC erratic

Hi all,
My HEVAC has been misbehaving for ages, but now it's bugging me more than usual, because of consistently hot weather (unusual in this neck of the woods).
Car is a '97 4.6 HSE. I've just had the AC regassed after replacement of a leaky section of tubing, so now I finally have cold air blowing from the vents, albeit occationally. The trouble seems to be connected with the outside air temp sensor. I replaced this some time ago, but the problem persists. 9 times out of 10, when I start the car after leaving it overnight, the HEVAC displays an outside temperature of -40C. In this condition it will not blow cold air, even if the temperature inside the car is more like +40C. After a while of driving, the outside temp reading will disappear altogether and then I can get cold air if I set the temp to LO. Now, with everything up to temperature, if I switch off the ignition and then restart, outside temp reading is correct and HEVAC functions faultlessly. The same will happen if I start from cold and drive for about an hour without stop. It will then stay OK for the remainder of the trip.

Any ideas? The temp sensor clearly works, and since the behaviour is so predictable, it doesn't seem likely that it's an intermittent contact somewhere.
Should I start looking for a replacement HEVAC panel?

Thanks!
Henrik
Bergen, Norway

There is a known problem with HEVAC unit JFC102400 fitted to vehicles with VIN WA381431 to XA417600 (see Technical Bulletin A/C 0011). The symptoms sound similar (I had the same sort of symptoms, but occurring more randomly). I am not sure if your car is in the affected range. The fault is in the HEVAC firmware. The cure is to fit the later part, JFC102550.

John

johnseedee said:

There is a known problem with HEVAC unit JFC102400 fitted to vehicles with VIN WA381431 to XA417600 (see Technical Bulletin A/C 0011). The symptoms sound similar (I had the same sort of symptoms, but occurring more randomly). I am not sure if your car is in the affected range. The fault is in the HEVAC firmware. The cure is to fit the later part, JFC102550.

John

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Hi John,
Thanks. My car is earlier in the range, with VIN VA369447. But I suppose it's still reasonable to suspect the control unit. I'll look around.

Henrik

Hi all,
Surfing for a cure, I stubled upon this:
95 96 97 98 Range Rover P38 A C Heater Climate AC Temperature Control Exchange | eBay
This seems to be the solution to my woes, but they're in the US. Clearly, there should be someone in the UK offering the same sort of service? How about Rovacom - the guys who do the BECM exchange service?

Henrik97 said:

Hi all,
Surfing for a cure, I stubled upon this:
95 96 97 98 Range Rover P38 A C Heater Climate AC Temperature Control Exchange | eBay
This seems to be the solution to my woes, but they're in the US. Clearly, there should be someone in the UK offering the same sort of service? How about Rovacom - the guys who do the BECM exchange service?

Click to expand...

There are lots of units on Ebay.

wammers said:

There are lots of units on Ebay.

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I know, but they're either new=expensive or used=not-guaranteed-to-work-for-any-length-of-time. This is the only place I've found that do an exchange service for a reconditioned unit with warranty. I was hoping there might be a similar service on offer closer to home.

Regards
Henrik

Henrik97 said:

I know, but they're either new=expensive or used=not-guaranteed-to-work-for-any-length-of-time. This is the only place I've found that do an exchange service for a reconditioned unit with warranty. I was hoping there might be a similar service on offer closer to home.

Regards
Henrik

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You pays your money and makes your choice. £690.00 max for a new one or a good S/H one from a reputable place like Emmotts. There will be some sort of limited warranty with one from there i would think. Get a JFC102550 if you do get a second hand one and you have heated seats or JFC102540 without heated seats. That is the latest version with the previous bugs removed.

Henrik97 said:

I know, but they're either new=expensive or used=not-guaranteed-to-work-for-any-length-of-time. This is the only place I've found that do an exchange service for a reconditioned unit with warranty. I was hoping there might be a similar service on offer closer to home.

Regards
Henrik

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Here is a new on at a good price !!

pmallinson said:

Here is a new on at a good price !!

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Fine if you don't have heater seats. And £168.00 cheaper than Rimmers.

wammers said:

Fine if you don't have heater seats. And £168.00 cheaper than Rimmers.

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I've got heated seats, but they don't work.....

Henrik97 said:

I've got heated seats, but they don't work.....

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Wires probably broken in the squabs. Easy fix but a bit of a ball ache to take the seats out and strip them down.

wammers said:

Wires probably broken in the squabs. Easy fix but a bit of a ball ache to take the seats out and strip them down.

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I know, which is why I haven't bothered yet. I read somewhere that the elements could be replaced by something much more reliable out of a Volvo, which is probably a good idea if one decides to dive in. Right now I can't be arsed, though, and I have a webasto in, so I don't really need them.

Cheers