after harddisk change fan is working at max

Known problem.

The wiring of Apple sensor connectors vary with the make of HD installed originally. These sensors may not work correctly on a different make of hard drive.

Best fix I've found is to install the free app smcFanControl

http://www.macupdate.com/app/mac/23049/s...

(might not work)

or pay $25 for hdd Fan Control

http://www.hddfancontrol.com/

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If your CPU fan is constantly running at full speed, as mine was, follow these instructions below:

Install smcFanControl

Go to the terminal and use these commands to regain control of your noisy iMac:

/Applications/smcFanControl.app/Contents/Resources/smc -k F2Mx -w 12c0

This will set the CPU Fan to max at 1200 rpm.

To revert to standard settings use:

/Applications/smcFanControl.app/Contents/Resources/smc -k F2Mx -w 3cf0

This will set CPU Fan to max at the default 3900 rpms

You might have noticed that the last 4 digits are the fan speed (in hexidecimal)

Other fan speeds you can try:

1100rpm = 1130

1500rpm = 1770

3900rpm = 3cf0

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Peter