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Aux Cooling Fan Issues

Discussion in 'E30 (1984-1993)' started by TSchager, Sep 7, 2018.

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    TSchager

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    I have a 1992 325ic. The air conditioning works fine but when I turn it on, the aux cooling fan, which should come on at low speed, does not operate. The fan also does not turn on when the engine gets hot. The resistor pack was changed in 2015 and the replacement (Magna) looks to be in good shape with no burning of the wires or the housing.

    Here's what I've tested:
    1) When the ignition is turned on and when the AC is turned on, I disconnect the 3 prong plug from the temp sensor located on the radiator. Bridging across the black/brown and green/black causes the fan to run at high speed. Bridging across the black and green/black does not turn the fan on at low speed.
    2) Swapping the low and high speed fan relays (K1 and K6) does not change anything.
    3) Fuses 19 and 3 are showing 12 volts.
    4) Fuse 18 does not seem to show voltage. This seems odd.
    5) For grins, I ran jumpers directly from the battery (positive and negative) to the resistor pack leads ahead and behind the cooling fan. This is a black wire. there are 2 wires running to the fan, a red and a brown. If I connect the jumper to the resistor connector between it and the fan, it comes on at high speed (12 volts). If I connect the jumper so voltage needs to go through the resistor, nothing. No voltage and the fan does not come on.

    I've done what I wanted not to do until knowing what is wrong by ordering a new resistor pack and a new thermo switch for the radiator. It seems the testing I've done would have bypassed the thermo switch as part of the testing but this is getting frustrating and maybe throwing parts at the problem will eventually solve the issue.

    Does anyone have an idea of what may be wrong? I'd really like to turn on my AC with the car running and have the aux fan turn on at low sped. Any help would be greatly appreciated.
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    MGarrison

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    You have the etm? 6454 is the wiring diagram, analyzing the circuit hopefully gets you there, but you'll probably want to look over the whole a/c system starting at 6410.

    http://wedophones.com/Manuals/BMW/1992 BMW 325i Convertible Electrical Troubleshooting Manual.pdf

    Not an issue I've had so don't know if I can offer much insight. If the way the low speed works is the resistor serves to reduce the voltage so the lesser voltage is the fan's low or normal speed and the resistor's out, then I guess it would be replacing the resistor.
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    TSchager

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    "You have the etm? 6454 is the wiring diagram, analyzing the circuit hopefully gets you there, but you'll probably want to look over the whole a/c system starting at 6410."

    etm? Wow, thanks for this link. I was looking for the wiring diagrams to understand the flow and parts involved to trace and diagnose. Thank you!
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    TSchager

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    ETM. Got it. Sorry to be so dense. PDF saved and page 95 printed. Time to do some checking. I sure hope the wiring harness didn't smoke when the original fan resistor fried when the prior owner had it replaced but will check C113 and the wiring. Thanks again.
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    TSchager

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    MGarrison,

    Thanks a lot for the link and the info. I did the following testing based on the advice and also based on the schematic:
    1) removed relay K1 and jumpered across terminals 30 and 87. Tested the impedance of the resistor without the key on. It showed 6 ohms. Turned the key and AC switch on and got 11 volts to one side of the resistor. The other side showed zero volts.

    2) Put K1 back in the relay position and repeated the test. No voltage when the key turned on and AC switch also on.

    3) repeated the jumper test where a positive and ground wire was connected directly to the battery. A jumper was also placed between the black and green black wire of the connector to the temp sensor on the radiator to remove the sensor/switch from testing. The fan runs at high speed with the jumper on the fan side of the resistor and nothing when the jumper is attached to the low speed side of the resistor.

    I am now assuming the system has a bad relay in position K1 and also a bad resistor. Do these assumptions seem correct? I guess it's possible there are issues with the connector at C113 but I have no idea where the connector is located.

    Thanks again for your help.

    Terry
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    MGarrison

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    Sounds logical to me, with the caveat I'm no expert on electrical. The ETM has component location and views, unfortunately sometimes the pictures aren't so great - see index on 9000-4 (p.140) & figure 5 on 7000-1 (p.105), that should get you to the connector to check from there. Presumably you saw the listing of the wiring color abbreviations on 3 (p.5), although the abbreviations are also pretty straightforward.
    • Member

    TSchager

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    Thanks for the tip on the index. I did see the color abbreviations. This document is priceless. Thanks again for sending the link.
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    MGarrison

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    TSchager

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    Yup. Got 2 of them. One in the car and the other in my office for reference. The Bentley doesn't come close to the detail the ETM provides. Both are great resources though. Thanks again.
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    MGarrison

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    Yeah, Bentley has some wiring diagrams, but not that one; got me curious to look, Bentley does have a chart of splice and connector locations, but no pics like the ETM. I don't know who hosts that wedophones site, but it's handy, has been there for a long time now & thankfully still is. Glad to be of any help!
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    MGarrison

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    • Member

    TSchager

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    Well, the plot thickens. It looks like the car has issues with grounds at the fuse/relay panel (Relay K1). I've changed out the resistor (it was bad) and the temp sensor (low speed trigger was bad). Turns out there's a link on Bimmerforms that talks about this problem.

    The link is: https://www.bimmerforums.com/forum/...ighlight=help with AC auxilliary Fan K1 relay. My pin 86 on the K1 relay was not going to ground. I created a jumper to K6 Pin 85 and fanned the leads out like it said in the blog.

    My car had exactly the same problem with pin 86 on K1, where the ground got disconnected somehow over time. Low speed operation on both temp and AC operation now work. High speed works too.

    In the end, the fix involved replacing the temp switch on the radiator, the resistor and the jumper. I suspect both the switch and resistor were bad due to a bad/failing ground on pin 86 that caused them to fail but we'll never know. Bottom line is that it is fixed thanks to your help and that of the link over on BimmerForums.

    This ought to be a sticky on the CCA website and forum because others have and will run into this. Debugging is a lot of work.

    Thanks again!

    Terry Schager
    MGarrison likes this.
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    MGarrison

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    Kudos on working it through & getting it squared - not easy w/ multiple issues like that!

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