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The March 2015 update of Apple's 13" MacBook Air features fifth generation Intel Core i5 and i7 processors, resulting in slightly increased performance and battery life.

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Fan running constantly at high RPM when adapter unplugged

Hi,

The fan on my MBA is running constantly when on battery, SMC Fan Control says CPU temp is 30-32 celcius and RPM is 6500.

As soon as I plug the adapter in, the fan starts slowing down and gets quieter until it settles at around 1200 RPM, and temperature still remains the same around 30-32 celcius.

I have reset the SMC and the PRAM/NVRAM. The OS is a fresh install (yes, I tried that too...) with no additional software on it except SMC Fan Control.

Everything else about this computer is working perfectly.

Update: Based on Dan's advice below, I have attached the TG Pro screen shot.

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Update (01/30/2017)

Thank you, Dan. I installed and ran TG Pro for a good few hours. Haven't used the auto boost mode yet, but might have to...

Anyhow, here is the main screen shot. It says one of the temperature sensors might not be working properly, but doesn't say which one and all the ones on the screen seem to be sending back data. Weird!

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Answered! View the answer I have this problem too

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I'm not a lover of SMCfan control software as I've had problems with it. In addition, you tend to burn out the fan's! I suspect the tachometer feedback for the fan is broken here. You'll likely need a new fan.

As to proving this remove SMC fan control software completely, then lets use a better tool here. Download this app: TG Pro it will allow you to see more clearly whats going on with all of the thermal sensors and fan in your system. For less than $20 US its well worth it! Once you have it running for an hour of so snap a screenshot of the main screen and paste it here for us to see.

Update (01/31/2017)

Now that we can see all of the thermal sensors within the system we don't have any high temps or bad sensors visible. The error message indicating you have an unknown sensor is telling me you have some corrosion on the logic board around the SMC logic.

Did you spill something into the keyboard at some point? Or sit the system down on a wet surface?

You'll likely need to pull the logic board out to inspect it for damage. Here's the IFIXIT guide you'll need to follow: MacBook Air 13" Early 2015 Logic Board Replacement.

Also check the fan cable to make sure its seated first to be doubly sure review Step7 before you pull the board.

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