iMac Fan Not Running

I have a 2006(?) iMac, Intel 2-Core Duo, Model Identifier is 'iMac5,1'

As far as I can tell the fan isn't running. I can't feel any air coming out the bottom, nor is there any sound that would indicate a fan running on the inside. It will frequently freeze up if I do something that requires complicated graphics, such as a video game. A hardware monitor program indicates that the GPU is heating up from about 50 degrees to 70 degrees in about 15 minutes of playing a game with 3d graphics (even though when the graphics are set on low quality).

Also, two different fan control applications (including smcFanControl) claim that the fans are running at about 800 RPM, but I don't think they are running at all.

Anyone know what might be wrong? Many thanks in advance.

Air is not supposed to come out of the bottom. Cool air is drawn in from the bottom and warm air is expelled from the top vents. If the fans were not running the machine would shut down very quickly. If you have SmcFanControl, set the fans to run at a higher RPM. If they refuse to run any higher than 800 RPM then you likely have a thermal sensor problem. And with a machine that old, it may not be worth repairing. You decide.

JimmyNeutron said:

As far as I can tell the fan isn't running.

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It probably is…just on low rpm.

JimmyNeutron said:

A hardware monitor program indicates that the GPU is heating up from about 50 degrees to 70 degrees in about 15 minutes of playing a game with 3d graphics (even though when the graphics are set on low quality).

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You didn't say if this is °F or °C.

JimmyNeutron said:

Anyone know what might be wrong?

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I would open the computer up & blow it out real good with compressed air. An older iMac like this can very easily be clogged up with a lot of dirt/fuzz.

- Nick

This probably will not be the most welcome news, but I should mention it anyway.

I own that very same 5.1 Core2Duo 2.1 Ghz White iMac. It was running great under Lion then one day I started to see artifacts that came and went. It got worse over time and the GPU temp would go way up and it would hard lock even with Facebook games! I did a search and found the ATI Radeon X1600's in those white iMacs are dying all over the place.

I got on Ebay and found a used but guaranteed Logic board for $50 and replaced the board. I had to use MY CPU from my old board. With the new board it's like new again and no more issues and temps doing the same games 20c lower.

@pigoo, The temperature is in celsius. If it was fahrenheit, I don't think 50-70 degrees would be much of a problem I'll try cleaning the dust out like you suggested.

@dtravis7, That is that of which I was afraid. There have recently been strange artifacts all over the place. The more complex the graphics, the more artifacts there were. This led me to believe it was a problem with the graphics hardware.

Thanks for the replies guys. If I resolve the issue I'll let you know.

JimmyNeutron said:

@pigoo, The temperature is in celsius. If it was fahrenheit, I don't think 50-70 degrees would be much of a problem

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I know that it may have seemed silly to ask if the temps were in °C or °F...but with some people you never know their expertise in diagnosing computer problems. And since you are a new member...I have no idea of your expertise level.

Also...I can almost guarantee that if you were taking a Chemistry or Physics exam...and didn't include the proper temperature units in an answer...you would lose points. So it's always good to be specific.

- Nick

Well, either the fan wasn't running at all, or like pigoo3 says, it was just a low RPM. In any case, I revved up the fans one at a time with smcFanControl and they all seem to be working okay. The problem seemed to be that they weren't coming on (or turning up) when they were supposed to. That's not so bad, as I can simply turn them on myself with smcFanControl.

What exactly would be wrong that would make the fans not come on when they are supposed to?

To repeat what I recommended above. Open the computer up…and blow it out with some compressed air. There are lots of areas dirt & fuzz can build up inside of the computer…especially after 9 years of use.

Clean out the computer…then lets see if the computer is operating properly or not. And then ask the question…what keeps the fans from coming on when needed.

- Nick

@pigoo3, I am definitely going to clean out the dust, although I don't know how that would keep the fans from coming on. The fans work properly, and the computer is also aware of how hot the various internal parts are getting (I used a hardware monitor to read the temperatures of various parts).

The fans in your iMac are controlled by thermal sensors. If those sensors are covered with dirt and dust they won't work right. Plus the fan blades could be impeded slightly by dirt or the fan bearings. Anyway, it won't hurt to do as Nick suggested. He's been pulling Macs apart and cleaning them since Henry Ford built his first car.

The fans are **designed** to run at a very low RPM, because the iMac is designed to use **convection cooling** in order to make the machine run as quietly as possible. Your fans are **working as designed** except that you keep mucking about them using SMC (which is completely unnecessary and can do more harm than good!). If your graphic card is going that's a separate issue, but by your own testing the fans are performing as designed.

Clean out the dust, uninstall SMC, and let's hope it isn't a graphic card issue (but I'm betting it is).

chscag said:

Anyway, it won't hurt to do as Nick suggested. He's been pulling Macs apart and cleaning them since Henry Ford built his first car.

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Ha ha Charlie. As time goes on…that statement feels more & more true!

But if this is true. Then you've been messing with computers since the dinosaur days!lol

- Nick