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Thread: Wiring when converting to non-A/C

  1. #1
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    Wiring when converting to non-A/C

    In the course of renovating my e21, I removed all of the air conditioning's mechanical components and the associated wiring. Now, years later as I am checking all of my electrical stuff, I find that the main blower speed switch (the one just below the hazard switch) does not operate the heater fan.

    I see that the plug that connects to the back of the switch has three wires: blue, yellow, black plus a brown ground wire. Those wires (except the brown) join the wiring harness and branch off to a plug connection embedded in the main blower box/unit (see first photo below).

    On the engine compartment side of the firewall, inside the cowl area where the heater fan lives, there are two wires connected to the motor's terminals: red and brown (second photo).

    My Questions:
    1. What happens in between these two connections?. From the wiring diagram (third photo), it looks like the "COOLING RELAY" may be involved in this magical transformation. During my removal of the A/C wiring, I cut the "gn/bu" wire that used to go to (or come from) the cooling relay (see the cut wire in first photo).
    2. Can any of you recall what rewiring you did when you removed your A/C?










    Last edited by dumbclub; 06-11-2012 at 01:21 PM.

  2. #2
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    I'm not 100% sure on this but I studied your picture and the wiring diagram. There is a wire that is cut in your picture. I suspect this goes to your heater fan. The cooling relay toggles who gets power. The ac blower if the switch is on or the heater blower if the a/c is not on. From there, both motors get there voltage drop across the fan switch. See if you have 12v at the cut wire.

  3. #3
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    OP, that green wire that was snipped is the fused "12v +" which is suppose to power the heater blower.

    Tbd

  4. #4
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    you are looking at the circuit wrong. most switches, if not all by BMW, provide a switchable ground not switchable power.

    so your heater circuit should be battery-fuse-blower-resistor board-(low/yl, med/bk, high/bu)-switch-ground.

    therefore the green/brown wire that is cut in your photo is the power supply to the blower motor, as Robert has pictured above.
    Last edited by Tom D; 06-11-2012 at 06:54 PM.
    Tom D

    77 e21 - m42
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  5. #5
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    [QUOTE]from ekr470:I'm not 100% sure on this but I studied your picture and the wiring diagram. There is a wire that is cut in your picture. I suspect this goes to your heater fan. The cooling relay toggles who gets power. The ac blower if the switch is on or the heater blower if the a/c is not on. From there, both motors get there voltage drop across the fan switch. See if you have 12v at the cut wire. [QUOTE]


    Nope.

    There is no voltage at the snipped gn/bu wire, but as I read the wiring diagram, it makes sense to me that there would not be any current there since the Cooling Relay is no longer "upstream" of it. I'm pretty sure that is part of what I eliminated when I took out the A/C wiring.

    Should I supply current to the snipped wire? Where should it come from?

    And back to my original question, what happens between that connector and the Blower Motor that has the red and brown wires at it's terminals?
    Last edited by dumbclub; 06-11-2012 at 07:05 PM.

  6. #6
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    the power needs to be rewired from the fuse to the green/brown wire that you cut.

    if you do a continuity test between the green wire cut and the red wire at the blower you will find that they are the same.
    Tom D

    77 e21 - m42
    88 e30m3
    04 330 dinan3
    84 r1000rt
    02 r1150rs
    all of them gray
    14 f800gsa - red headed stepchild!

  7. #7
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    Quote Originally Posted by Tom D View Post
    the power needs to be rewired from the fuse to the green/brown wire that you cut.

    if you do a continuity test between the green wire cut and the red wire at the blower you will find that they are the same.
    Thanks Tom.
    I was pretty sure that you would weigh in on this electrical problem thread. Do you happen to know where the harness under the dash has a easy connection point for this? I find it is easier for me to relate to actual physical locations rather than points on a wiring diagram. I am easily intimidated by electrical dilemmas.

    Quote Originally Posted by dumbclub View Post
    And back to my original question, what happens between that connector and the Blower Motor that has the red and brown wires at it's terminals?
    To elaborate, I'd like to understand how those blue, yellow and black wires go into the heater box on the passenger compartment side and come out on the engine compartment side to the fan as red and brown wires. Obviously there is some relay or other device inside there, but I don't see it on the wiring diagram.

    The main thing is, I'd like to reconnect that snipped green (w/blue stripe) wire to it's proper source of power, not just rig up a new wire from the fuse box. Does anyone know how that is wired from the factory? Looking at the wiring diagram, there should be a green/brown wire coming from the fuse that supplies the power, but I don't know where on the wiring harness it is located.

    Thanks for everyone's help on this.


    Success !


    The solution was easy and as usual, I was making it much more complicated than necessary.

    The wire supplying the current to power the blower motor is only a couple of inches away from the end of the wire that I had snipped when I removed all of the A/C wiring. To make the heater blower work after removing the A/C, I just needed to connect these two wires:







    I now have a fully functional fan blowing cool breezes through the car.

    Many thanks again to all who responded and helped me see what was right in front of me.
    Last edited by dumbclub; 06-12-2012 at 11:38 AM. Reason: Automerged Doublepost

  8. #8
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    Thank You

    My heat has been nonoperational since buying it 5+ years ago. This thread was the answer! My A/C doesn't work, but the ac blower wouldn't stop running. I simply cut and connected like above and BINGO! My heater blower runs and I have heat! Thank you!!!

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