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Thread: Troubleshooting cooling fan

  1. #1
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    Troubleshooting cooling fan

    I was installing Dave's electronic fan relay when I noticed my front left fan (original fans still in car) was not running. Nothing to do with the new electronic relay (which works great). So I did some troubleshooting:

    1. Unplugged the left fan and connected it to a portable 12 VDC source - fan runs just fine.
    2. Measured the voltage at the plug supplying current to the fan (with fan disconnected - multi-meter probes in plug). Indicated 6.8 volts.
    3. Measured the voltage from the positive plug prong to frame ground of car. Same, 6.8 volts.
    4. Measured ohms resistance from negative prong to frame. Low, around 0.3 ohms.
    5. Measured voltage leaving the fan fail socket (I still have fused jumpers in socket) with negative lead referenced to negative battery post. 12.5 volts.

    A little perplexed about the voltage drop. How could I get 6.8 volts at the fan connector with just the multi meter plugged in (essentially no load)? The right fan is working normally. Ran out of time (how's that possible with a DeLorean?) and had to put this aside for later. Perhaps someone has a tip on this.

    Thanks,
    Ron

  2. #2
    Senior Member Bitsyncmaster's Avatar
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    Yes that is very strange to see a voltage drop without a load connected. Are you sure your meter did not auto range to another scale so you did not really see 6.8 volts?
    Dave M vin 03572
    http://dm-eng.weebly.com/

  3. #3
    Admins Never Retire Ron's Avatar
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    Quote Originally Posted by DMC-Ron View Post
    5. Measured voltage leaving the fan fail socket (I still have fused jumpers in socket) with negative lead referenced to negative battery post. 12.5 volts.
    Did you check it at the socket's terminal itself (v/s the terminal that plugs into it from the fused jumper)?

    I'd try connecting everything up then swapping the two fused jumper terminals....
    Or, bypassing the socket's terminal by applying 12V to the BG wire immediately after it...

  4. #4
    Senior Member Bitsyncmaster's Avatar
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    Most fuses you can touch a pointed meter probe on the little metal tabs on the top of the fuse to measure the voltage under load.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  5. #5
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    Ron and Dave,
    Good suggestions. It occurred to me that the connector in the fan relay socket might have backed out. I felt underneath and there didn't seem to be anything pushed back. From the top it looks fine. I'll check it again then measure it under load. I'm also going to extend a wire to the battery ground lug so I can see actual plus voltage at the fan plug. Later, I can switch and use the same wire for the + voltage and tap from the relay socket to the fan.

    The multi-meter is new to me (I purchased one with dwell) but it is not auto-scale, so I think the 6.8 volt reading was valid. I'll verify with my fluke.

    Later,
    Ron

  6. #6
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by DMC-Ron View Post
    Ron and Dave,
    Good suggestions. It occurred to me that the connector in the fan relay socket might have backed out. I felt underneath and there didn't seem to be anything pushed back. From the top it looks fine. I'll check it again then measure it under load. I'm also going to extend a wire to the battery ground lug so I can see actual plus voltage at the fan plug. Later, I can switch and use the same wire for the + voltage and tap from the relay socket to the fan.

    The multi-meter is new to me (I purchased one with dwell) but it is not auto-scale, so I think the 6.8 volt reading was valid. I'll verify with my fluke.

    Later,
    Ron
    I have used a long meter jumper wire to find voltage drops for my fuel pump. It's a great way to get the ground reference clipped right on the battery terminal so you can find voltage drops with one solid reference point.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  7. #7
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    A little further troubleshooting on this issue and I have found that I have 22K ohm resistance in the wiring from the fan fail relay socket to the + side of the fan connector.

    But let me back up a bit. Previously I found that if I injected +12 volts into the fan connector the fan would run. This verified the fan ground was fine (I thought for sure it was probably a grounding issue). Here is the probe supplying +12 to the fan (nothing disconnected at this point):
    PA272325.jpg

    If I connect my meter at the fan fail relay and the disconnected fan plug for a continuity test I see the 22K ohms of resistance:
    PB202319.jpg PB202326.jpg

    So my questions: Would it seem likely that the resistance is a poor connection? What would be the most likely cause and location for this issue (bad connection??)? This is the left cooling fan green/black wire between the fan fail relay and the left cooling fan connector. When I look at the wiring schematic, I see connector designations shown but it's not clear if the represented connectors are in the wiring harness or if the connector shown in the circuit represents the connector right at the cooling fan. More to the point, are there any connectors in the wiring harness I should focus on?
    Cooling Fan Wire Schematic.JPG

    I would appreciate your suggestions,
    Ron
    Last edited by DMC-Ron; 11-20-2017 at 05:11 AM.

  8. #8
    Senior Member Bitsyncmaster's Avatar
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    The fan wires run from the fan fail socket up to the connectors near the washer bottle. Your bad connection could be the contact area of those washer bottle pins or a crimp on those pins. It could also be the crimp on the fan fail socket pin or the two pin fan connector pin.

    The washer bottle connectors are a pain to get at so I would start with new pins on the two pin fan connectors and fan fail socket pins.

    Note the stock wiring is non-plated copper wire so when I replace a pin, I sand paper the striped wire to get clean copper.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  9. #9
    Admins Never Retire Ron's Avatar
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    The connection near the washer bottle would be my guess for a bad connection causing it. But, like Dave,
    I'd eliminate the rest first...Maybe get a couple of straight pins and pierce the ends of the Black/Green and Black/Orange wires immediately behind where the connectors crimp to the wire and take a reading.


    Probably nothing, but just to be sure- In the 3rd pic, the Red wire in the fan fail socket goes to the meter's
    probe lead, and, the meter's common connection is not in a pic. I.E. The Black wire shown is NOT going the meters common lead, but into the cooling fan relay socket from a previous test??

  10. #10
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    Quote Originally Posted by Bitsyncmaster View Post
    The fan wires run from the fan fail socket up to the connectors near the washer bottle. Your bad connection could be the contact area of those washer bottle pins or a crimp on those pins. It could also be the crimp on the fan fail socket pin or the two pin fan connector pin.

    The washer bottle connectors are a pain to get at so I would start with new pins on the two pin fan connectors and fan fail socket pins.

    Note the stock wiring is non-plated copper wire so when I replace a pin, I sand paper the striped wire to get clean copper.
    Dave,
    OK. I'll take a closer look at the relay pins and the fan connector. But just from looking they seem fairly good, at least not a lot of corrosion.

    Here's a close look at the fan fail relay socket:
    Attachment 54630

    Another odd thing that has me scratching my head is the connector at the left fan. The connector appears to have two wires connected to each pin. It looks like the power wire (black-green) comes into the connector then cascades out heading somewhere else? Same with the ground wire. Why would there be two and where are they going? I may just not be seeing this correctly. Perhaps when I clean up the wiring area it will look different Here's a picture in hopes that you can see what I'm talking about:
    Attachment 54631

    Also I notice that the fan connector is coated with a protective grease. The Good news is that there is no corrosion. I like to use Corrosion X on electrical connectors but I know others use various conductive grease products. Here's a photo:
    PA272360.jpg

    Anyone have pictures of the connector at the washer bottle?

    Thanks, Ron

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