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Old 08-05-2010, 11:43 AM   #1
JJDetroit
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Ford Focus Cooling Fan problem defies all logic diagnostics

Ok so I am a total noob and my first post will hopefully not be written-off, I did search the site and have spent about 10 hours or so readin through the different overheating threads. I am going to tryto be as detailed about my problem as I can without writing a book.

On one of the hottest days in Detroit this year about a month ago, I had 5 adults in my ZX3 in the rain with the AC on Full Blast Recirc. As I was stopped to drop off the other four, the AC stopped blowing cold and my windows fogged over. I drove about 3 blocks before I saw the temp needle all the way in the red. I parked and left the car there overnight to cool off. Next morning I tried everythign AC on/off, idle, everything and the car would not overheat and AC was cool. So I chalked it up to overworking the system and went about my buisness.

Over the last few weeks the AC has been intermittently cold, then warm, then cool. Also on the hottest days ehn stuck in stop and go traffic, about 3 times the car would start to overheat, but by gettng moving or turning the heat on full blast I was able to cool it down enough to get home, next morning, no problems.

So now I am pretty sure the fans are not working properly. I read all about the fan resistor issues alot of had (pulled, inspected, and tested mine - no issues there) plus turning on the AC did not cool down the car. I finally got it overheat in the garage and check and the fans were not turning on.

SO next step, I disconnect the fans and try to jump them directly from the battery, the driver side fan was dead even when I put 14 volts right to the terminals on the motor. (ok I need a new fan).

Here is where it defies all logic. I jump the passenger side fan with wires direct from the battery and it spins. I checked all the relays and they are working great. So now I place a voltmeter on the other side of the fan connector and it measures 14v. I plug this into the fan - nothing. How is is possible that supplying the motor with 14volts directly from the battery via jumper spins the fan, but when I plug in the harness which is reading 14volts just like the battery jumper, the fan doesn't come on? IT makes no sense to me.

I ordered a new fan assembly today since the driver fan motor was shot, but I am nervous that the passenger side fan might not work.

Sorry for the length of this thread, bt thanks in advance for any thoughts you guys might have.

I have already used this forum to help me diagnose and now how to remove the fan assembly. It has been super helpful.


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Old 08-05-2010, 12:46 PM   #2
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Sorry for the spelling above, it was typed in a hurry.
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Old 08-05-2010, 04:36 PM   #3
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JD, you need to not always think of Voltage as the answer, that's just the power rating, it take amps to make an electrical device to work, being the pushing power behind electricity, connecting directly to the battery gives you full access to all the amps in the cell, check the connection is delivering enough amps grunt (the fan relays control that), if not it could still be a faulty motor and the extra amperage you get connecting directly is enough to get the fan to spin. Check the resistance across the terminals of the fan too, a very high resistance will point to the armature may be starting to burn out.
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Old 08-05-2010, 10:41 PM   #4
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Posted via FF Mobile iMHO - The first response was on the right track as to why no operation despite 14 volts at the plug in. A sensitive meter will see voltage, when load applied voltage would drop to near zero in this case if measured with fan plugged in - poor connection somewhere allows enough for a no -load voltage to be measured, but won`t run the fan. A test light helps diagnosis in this case - meter will show volts, but test light won`t light. It`s a been there - done that for me, liked using a meter for everythting, then I found cases where I was fooled by seeing volts, yet nothing worked. Voltage fine, test light wouldn`t light boggled the mind `till I realized the meter would register without needing even the small current needed to operate the test light bulb.....
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Old 08-05-2010, 11:32 PM   #5
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First check to see if you have resistance on the fan pins if you have an electrical meter that will show ohms. I don't know the exact figure but it should be more than 1 ohm, and not as much as 100. If you can't find any resistance on the fan motor leads- then it's toast. If you do find resistance on both leads, then find your grounding point for that circuit, and make sure it is good.

One more thing, did you try reversing polarity when you couldn't get the fan to come on through the harness? There might be a diode in there, and if you have it reversed- that will block flow.
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Old 08-06-2010, 08:02 AM   #6
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Thanks for the advice. I picked up my new fan assembly this morning ($125). I could have gotten one from ebay for $103, but it was worth the extra 20 for me to get it the next day. I will try installing the new fan assembly tonight, hopefully that is the only issue.

Anyone know how I can check the amperage? Will a multimeter (nice digital one) apply a load to check amps?

Also, can you guys tell me which is the high speed fan versus low speed? If I idle the car up to running temps and turn on AC should that trigger both fans? Just trying to check to make sure both fans are working properly.
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Old 08-06-2010, 08:45 AM   #7
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Posted via FF MobileTest light at unplugged connector to see if circuit will pass some amperage. The Quality VOM is the problem in this case, it`ll read voltage (electrical potential) without drawing power (amperage). Great for testing electronics, not always useful on power circuits.
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Old 08-06-2010, 08:54 AM   #8
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I think the AC only powers one fan. We suggest turning on the AC only when neither fan runs at all- or when those fans only run at full speed when the resistor pack is bad. This prevents cars like that from overheating.

You can test amps with a clamp on ammeter, but there's some confusion about how electricity works on this website. Amperage, or current, is a result of electrical work, not something that can be increased or decreased at will. When you lack current, your problem is most certainly the connection to the power source, or the source itself. My personal confusion comes from cars being a battery fed power source whereas at work I'm used to power without those limits. When you connect insufficient power to an electrical device, everything drops out, and the end result is that nothing happens.
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Old 08-06-2010, 09:12 AM   #9
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I'll give the test light a shot tonight to see if I get a light before plugging in the new fan assembly.
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Old 08-06-2010, 09:51 AM   #10
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Posted via FF Mobile Pressure & volume of water flow often is used as an analogy for electricity. pressure = voltage volume = amperage In this case (voltage but fan doesn`t spin) it`s like a pinhole in a hose - coming out fast, but not enough volume to DO anything with. A guage would show 60 psi or more yet hardly enough volume to spin a pinwheel toy.....any resistance will easily deflect the stream or stop it altogether..... Electrical meter shows that voltage (pressure) is present, but the connection might be like that pinhole, not enough volume avail. to turn the fan.....
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