AC wiring question- Diode?

Discussion in 'E9 Projects and Restorations' started by m5bb, Apr 4, 2019.

  1. m5bb

    m5bb Well-Known Member Site Donor $

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    I know this goes in the AC circuit and I think I know where but just want to verify.
    Another time I didn't take enough photos.
    I think it goes in the line coming from inside the car that goes to the off/on switch to the compressor?
    I believe it is a diode and is marked with an arrow I guess meaning the current flow?
    So 12v is coming through switch when closed and going to clutch on compressor to turn it on?
    So that is the current flow.
    BTW the diode is not shown on the wiring diagram. The "flying fuse" is.
    Verification please.

    Picture uploads are not working today. I tried at 9 AM and now at 1PM.

    So hopefully someone will know what I am talking about and can help me.
    TIA,
    Gary
     
  2. Simufly

    Simufly Well-Known Member

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    I have the same problem, flying fuse to be installed but where?
     
  3. Stevehose

    Stevehose Well-Known Member Site Donor $

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    The fuse to the compressor is an inline one located where the wire comes out of the nose clip along with the ac hoses. The only reason I see to need a diode is if you are using your condensor fan as a backup fan if the radiator gets too hot (activated by a temp switch in the thermostat housing), then you would need a diode to prevent voltage from back feeding to the dash switch.
     
  4. Ohmess

    Ohmess I wanna DRIVE! Site Donor

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    Steve -- In my car the fuse is in line from the battery to terminal 30 of the fan relay. It only fuses the cooling fan in front of the condensor. Both the blower motor and the magnetic clutch on the compressor are fused off switched power at fuses 8 and 9.

    My car is a 72; I think later cars had a different wiring configuration.
     
  5. m5bb

    m5bb Well-Known Member Site Donor $

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    The fuse I got. The "flying fuse" as BMW calls it.
    Still won't let me upload a photo.
    So can't show what I am talking about.
     
  6. Stevehose

    Stevehose Well-Known Member Site Donor $

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    You’re right, I was mistaking the condenser fan fuse for the compressor. But the fan will have to have a diode if it is going to pull double duty.
     
  7. HB Chris

    HB Chris Well-Known Member Site Donor $$

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    I think 74 was the first year with a temp sensor in bottom of radiator to energize condenser fan, with this setup a diode is needed.
     
  8. m5bb

    m5bb Well-Known Member Site Donor $

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    As you know nothing is stock about my setup.
    I have a radiator from a E28 535 I think? PO did this and radiator is in good condition.
    Switch is at top passenger side and this setup worked before I just didn't document where this diode went 3 years ago. My bad.
    So the diode goes in the line from the auxiliary fan to the relay which is near the coil on the passenger side?

    Just tried and site still won't upload a photo.
     
  9. HB Chris

    HB Chris Well-Known Member Site Donor $$

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    I have Don’s instructions for this somewhere
     
  10. sfdon

    sfdon Well-Known Member

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    Diode pic- can’t download......
     
  11. m5bb

    m5bb Well-Known Member Site Donor $

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    Me too. I've been trying to load a photo for 2 days now. ????
    I got it figured out. The cute little diode in it's case goes in the +line from the aux fan before it attaches to the relay. It (the fan) would act like a generator and could keep the clutch engaged when it shouldn't be.
     
  12. sfdon

    sfdon Well-Known Member

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    No.
     
  13. m5bb

    m5bb Well-Known Member Site Donor $

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    Correct answer is?
     
  14. sfdon

    sfdon Well-Known Member

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    I’m in Austin firing up a car and visiting Terry Sather. Dinner time and then a drive in hill country.
    I’ll check my iPad for a pic later.
     
  15. m5bb

    m5bb Well-Known Member Site Donor $

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    Here's the diode I've been trying to upload for 2 days.
    I just need to know where in the circuit it goes. You said no to 12v line to aux fan. So my next guess is the line from the dash switch to the compressor?
    Some how I lost how the temp sensor in my radiator gets connected as well. My rad is from a 535 i believe but same idea as later E9's.
    Sorry I messed this up but doesn't seem to be a diagram with the diode shown. Not that I can find.
    Tell Terry I said hi. I talked to him some at Ofest in Colorado in 2014 when I got the Parker Spooner Award for my coupe. It didn't really deserve at that time but it pays to show up.
     

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  16. HB Chris

    HB Chris Well-Known Member Site Donor $$

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    from Don
     

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  17. m5bb

    m5bb Well-Known Member Site Donor $

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    Thanks Chris. I'll give that a try tomorrow.
    Now I'm trying to find the black tach signal wire that is supposed to be near the coil. Unfortunately it only goes to the tach and you know what that's like to get to.
    I wrapped my harness all the way over to the coil side just behind the headlight. I found a black wire with a spade connector coming out of the harness but now have to get to the other end to see if that's it.
     
  18. HB Chris

    HB Chris Well-Known Member Site Donor $$

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    When I did the b35 that was one of the seven wires from the engine harness that I tapped into the chassis harness in front of the driver.
     
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  19. sfdon

    sfdon Well-Known Member

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    Black wire goes from:

    Distributor to Coil
    From coil to diagnostic plug to tach
    From coil to engine speed switch
     
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  20. m5bb

    m5bb Well-Known Member Site Donor $

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    Got it figured out. Found black tach line at diagnostic connector and am going to make an assumption that it is going to the tach.
    I was extremely careful hooking up the instrument cluster knowing that getting back in there was no easy task.
    So I hope the ass in assumption does not bite me in the but.
    Everything else got wired thanks to Don's diagram or was that Chris? . Can't start yet as I'm waiting on my headers to be ceramic coated. They had been done when I rebuilt the engine in 2014 and then sat for 3 years and when I got them out and cleaned up they look used, unlike everything else on this car so $220 dollars more to the tab. At least that seems reasonable compared to the $200+ that BMW wanted for a drier.
    Thanks again Don and Chris for the help. This car was such a mess from PO sloppy wiring and missing items that it's all getting straightened out now.
     
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