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P38A Weird Hevac thing

Discussion in 'Range Rover' started by Digweed, Oct 25, 2018.

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  1. Digweed

    Digweed Member

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    I've never had the heater/ac control unit working at all, not even lighting up. I found on RAVE what the power supply pins were. I pulled out the unit and disconnected the plug, white connector C0792. When I turned on the ignition to test to see if there was even power going to it the fan came on, went off when I plugged the connector back in. I have two HEVAC control units but there's nothing to say that both of them are buggered, is there something that I'm missing? I'm getting ~2.3V on pin 3 forgot to test pin 2 so I don't know if there's anything there:mad::mad::mad:!!! I've sourced another unit but won't have it for a couple of days so I'm just seeing if there's anything else. Could I just put 12V across pin 2 + 4 and 3+4 and see if it even lights up?
     
  2. Datatek

    Datatek Well-Known Member

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    Have you checked the fuses?
     
  3. wammers

    wammers STILL BREATHING. Donater

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    If it's just the LCD display not showing make sure the backlight bulb is good. Bulb with green holder in middle of LCD back cover.
     
  4. Digweed

    Digweed Member

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    Nothing at all works on it. Can't change fan speed, direction or temp.
    And double checked. There was a small voltage on pin 3 about 2v, forgot to check pin 2!
     
  5. wammers

    wammers STILL BREATHING. Donater

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    What is the part number on the back of the unit. Yours should be JFC102550 that is the latest version. That version will work retrospectively on older cars but some older units will not work on newer cars.
     
    Last edited: Oct 26, 2018
    Digweed and Joss155 like this.
  6. Digweed

    Digweed Member

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    Cheers I'll have a look at that when I'm back at it next week.
     
  7. Digweed

    Digweed Member

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    Sorry for the delay inn this. Got a replacement unit for this with the jfc part number. Still nothing showing on the screen and can't change fan speed, temp or anything. None of the buttons work. It started raining heavy while i was at it so i didn't get a chance to have another look at fuses and relays.
     
  8. Datatek

    Datatek Well-Known Member

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    So obviously no power to the HEVAC. Replacing it is an expensive way to prove it.
    If you look at CO792, the white connector, pin1 is fed with 12 volts from the BECM relay 7 and fuse F8 30amp.
    pin 2 is fed from the engine compartment fuse box F42 10 amp.
    pin 3 is fed from the engine compartment fuse box F35 10 amp.
    pin 4 is ground.
     
  9. Digweed

    Digweed Member

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    I'd checked pin 2 and 3, hadn't found pin 1 on rave. I'll check it the next day I'm back at it. From what i remember I'd 12v on 2 and a small voltage on pin 3 about 2v. I'd continuity with pin 4 and ground.
     
  10. wammers

    wammers STILL BREATHING. Donater

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    Check all the fuses listed by Keith, if it's not being powered it won't work.
    Pin 1 is Auxiliary power input.--------12 volts with ignition.
    Pin 2 is Battery power input.--------- Permanent 12 volts
    Pin 3 Ignition input.---------------------12 volts with ignition on.
    Pin 4 Ground.
    Pin 5 Screen heaters output.-------12 volts when selected.
    Pin 6 Illumination input.--------------12 volts feed with lights on.
    Pin 7 A/C Clutch output.-------------12 volts with A/C on.
    Pin 8 Condenser fans output.------12 volts with A/C on.

    Pin 1 is at left of socket next to L/H orientation notch. Pin 3 is next to R/H orientation notch. Pin 4 is above pin 1 and pin 8 is above pin 3.

    So basically it is, looking at socket
    4 5 6 7 8
    1 2----- 3
    \-----------/
     
    Last edited: Nov 15, 2018 at 10:58 AM
  11. Digweed

    Digweed Member

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    Got a look at this today. Pin 2 is showing 12v permanent. Pin 3 is showing about 14v with engine on. Pin 1 is showing 2.47v with ignition on. Am i looking at a dodgy relay not making good contact? I've continuity with pin 4 and ground. I didn't test the rest of the pins as the unit isn't powering up.
     
  12. Datatek

    Datatek Well-Known Member

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    Look at RAVE for details of the wiring, the relay is in the BECM I believe, in which case it may well be a corroded connector on the BECM or on the fuse holder.
     
  13. wammers

    wammers STILL BREATHING. Donater

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    Power to pin 1 with ignition is from BECM Fuse 8. 30 amp via relay 7 in BECM.
     
  14. Datatek

    Datatek Well-Known Member

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    see post #8o_O
     
  15. wammers

    wammers STILL BREATHING. Donater

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    Have seen that Keith. Maybe he didn't, you seemed unsure in post 12 so just confirmed it.;)
     
  16. Digweed

    Digweed Member

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    I've had the BeCM out a few weeks ago and gave it a good cleaning with contact cleaner. I'll pop it out again to have another look. Is there any way to test the relay on the board? I'm getting 12v across fuse 8 under the seat.
     
  17. Digweed

    Digweed Member

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    After having a read of rave there. It said...

    Ignition position 1 (Accessories)

    This feed is obtained from the BeCM via fuse 8 and is shared with the Radio, Front cigar lighter and car phone (if fitted). The Ignition 1 is essential to the control panel as it provides power to the ECU although no functions or display on the LCD are possible.


    The radio works no problem, once I got the code for it that is.
     
  18. wammers

    wammers STILL BREATHING. Donater

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    If radio works check for 12 volts at cig lighter. If power to cig lighter relay 7 is fine. Problem is from splice S212 to pin 1 of plug or a break in the wire between S212 and pin 1 on plug. You can jury rig a connection from cig lighter power to pin one and see what you get. No shorts though be careful.
     
    Last edited: Nov 13, 2018 at 10:05 AM
  19. Digweed

    Digweed Member

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    Thanks for that suggestion, was going to try it from the radio feed but the cig lighter is much better! Thanks.
     
  20. wammers

    wammers STILL BREATHING. Donater

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    Yes much easier.
     
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