CPU fan issue
March 17, 2014 5:14 AM   Subscribe

The fan on my CPU cooler is blowing in the wrong direction!

After last week's problem I bought a new graphics card. On installing it I noticed that the fan on my tower CPU cooler is blowing in the wrong direction: away from the heatsink and into the case.

My CPU cooler is an Arctic Freezer 13. The arrows on top of the heatsink indicate the direction air is supposed to be flowing, but it is not obeying.

It does not appear possible to remove the fan and face it in the other direction; it is designed to fit only one way.

To the best of my knowledge, in my previous motherboard this was not a problem; the same heatsink cooled a heavily overclocked Core 2 Duo without any issues. If it has been blowing in the wrong direction since I installed it in my new(ish) motherboard, this would go some way to explaining why the temperature of my 8350 has always been only slightly lower than it was with the stock HSF.

Is it at all possible to reverse the direction of this fan? Or am I going to have to shell out for a new CPU cooler too?
posted by ArmyOfKittens to Computers & Internet (24 answers total)
Is the CPU actually overheating? If not I really wouldn't worry that much - whether it makes any difference probably has more to do with the overall airflow inside the case than anything else.

Unless you're overclocking the thing within an inch of it's life of course, in which case maximally even cooling might actually matter.
posted by pharm at 5:33 AM on March 17

That fan is dispersing the heat by pulling it away from the heat sink and blowing it into your computer case. In other words, it's pointing the right way!
posted by Mothlight at 5:36 AM on March 17

Or am I completely wrong about this? Now I'm wondering.
posted by Mothlight at 5:38 AM on March 17

Either way works, which way is best depends on the design of the heat-sink.
posted by Akke at 5:47 AM on March 17

However, looking at the image of this cooler in question. The fan is actually on the side of the heatsink. In this case, the fan should be blowing towards the rear of the case.
posted by Akke at 5:52 AM on March 17

Yeah, if it was designed to blow the heat away I wouldn't be worried. But the arrows on top of the heatsink indicate the intended air flow direction, so I have to assume it's working below its maximum potential.

The 8350 is a hot chip at the best of times, and with the cooler the way it currently is it's over 60C after about a minute of priming, with no overclock.

It'd be nice to OC the chip since I have a motherboard that can deal with its monstrous power requirements, but right now I'd settle for getting the temps under control.
posted by ArmyOfKittens at 5:54 AM on March 17

From the picture, the fan should be rotating anti-clockwise, so the blades scoop the air onto the heat sink. Is this what you see? If it's rotating clockwise, then I think something is wrong.
posted by carter at 5:54 AM on March 17

carter: "From the picture, the fan should be rotating anti-clockwise, so the blades scoop the air onto the heat sink. Is this what you see? If it's rotating clockwise, then I think something is wrong."

In that case, something is definitely wrong!

I'm starting to think this might be another one of those "just replace it" scenarios.
posted by ArmyOfKittens at 6:06 AM on March 17

If it's rotating clockwise - that is with the convex side of the fan blade leading - then it's just pushing air around somewhat randomly. Did the fan come prewired? I would contact their tech support and describe the situation and what you did to install the fan so far.
posted by carter at 6:19 AM on March 17

I don't think it's physically possible to do so but could the fan be plugged into the motherboard the wrong way? Or maybe plugged into a case fan power lead instead of the CPU fan lead? I'm not even sure that should make a difference but who knows.
posted by Venadium at 6:30 AM on March 17

Yes, if it's possible to be plugged in the wrong way, the polarity of the motor might be reversed, causing it to spin backwards. I'm not an expert though.
posted by carter at 6:35 AM on March 17

Yeah, the fan came as a complete clip-on package. I emailed their tech support but since the whole thing is a long way out of warranty--I bought it to overclock a Core 2 Duo after all!--I'd be surprised if their response was much more than "buy a new one."

The fan connecter is notched where it plugs in to the motherboard, preventing me from plugging it in the other way round. It's also very short, which prevents it from reaching the case fan connectors, which are on the other side of the motherboard. I suppose I could buy an extension cable, but if I'm spending money I'd be at the point where I might as well buy a new fan and fit that to the heatsink.
posted by ArmyOfKittens at 6:40 AM on March 17

Actually, looking into a little more, it looks like most CPU and case fans won't reverse direction if the polarity is reversed. My guess is that it was assembled wrong at the factory and has been spinning this way since you got it.
posted by Venadium at 6:53 AM on March 17

That seems most likely!

From this point I'm looking at replacements, whether of the whole HSF unit or just the fan.

Thanks for your help, everyone :)
posted by ArmyOfKittens at 6:58 AM on March 17

It does not appear possible to remove the fan and face it in the other direction; it is designed to fit only one way.

I am assuming that this is an AC (induction) motor. An induction motor is perfectly happy spinning in either direction. Just reverse the wires and it should spin in the opposite direction.
posted by three blind mice at 7:40 AM on March 17

Ooh, I will definitely give that a try when I get home, thanks!
posted by ArmyOfKittens at 7:44 AM on March 17

The fan is almost definitely 12 or 5V DC with a PWM control pin, not AC. I've never been able to get a cooking fan to spin backwards, but I haven't worked with this exact model, so YMMV...
posted by drapatz at 7:56 AM on March 17

Replacing the fan is not a big deal, find one of a similar size (92mm) and stick it on there, using two part epoxy putty or zip ties or some wire etc. There is usually an arrow molded on the case of the fan showing which way it blows air if you can't tell by the blade shape. Make sure it's blowing into the heatsink.

As to it blowing the wrong way, there is a little controller inside the fan which controls direction, you can't simply reverse the polarity of the feed. This is a screwup in manufacturing, and I'm surprised their QA didn't catch it. (You could theoretically find the controller and reverse the output in there, but it's easier to buy a new fan)
posted by defcom1 at 8:45 AM on March 17

Am I right in thinking that for something like this I should be looking at a specific sort of fan? I was under the impression that there were essentially two kinds of fan: one that blows a wide dispersal of air, suitable for use as a general case fan, and one that has a much narrower focus, to push air through heatsinks. I'm not entirely sure how to tell them apart!
posted by ArmyOfKittens at 8:55 AM on March 17

Ah, looking over I guess I should be looking at high (30+) CFM PWM fans.
posted by ArmyOfKittens at 9:03 AM on March 17

Fans with smaller blades, closer together work better for higher backpressure, which is what you get when you put it on a heatsink. But, really, when it comes to computer cooling fans, you can overthink it. If you want more airflow, put a second fan on the opposite side, pulling, and just call it a day.
posted by defcom1 at 9:08 AM on March 17

Sounds good, thanks.

I'll pick up an appropriate fan or two when I'm in town, then.
posted by ArmyOfKittens at 9:11 AM on March 17

The connector to your fan should be wired like this.

If the ground and +12V wires are reversed in error, the fan would run full-on all the time through the body diode of the PWM FET, except backwards. The PWM speed controller and tachometer would not work. If that is the case, you need to swap red and black to their proper positions.
posted by JackFlash at 9:54 AM on March 17

I believe best practice is to have two fans, one pushing and one pulling, so you get airflow through the case - there should be a space for another at the front of the case.

Also, reapplying your thermal paste is a possibility to improve that temperature.
posted by Sebmojo at 5:38 PM on March 17

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