BrokenFanControl is a simple program to set the maximum fan speed in a Mac Mini.

Introduction

It's not useful for everyone and can be dangerous for your computer. I needed it because I broke a temperature sensor in my Mac Mini Server (Mid-2010) changing one of the internal drive for a Crucial m4 (a great drive, btw). Therefore the fan was always starting at full speed and this was really annoying.

All fan control programs are designed to raise the minimum fan speed to cool more while my problem is the opposite: lower fan speed (allowing the computer to raise its temp). So I decided to run my own (building on work already done by others).

WARNINGS

This program is not meant for regular users. It is for hackers, people who know their Mac and are not afraid of it, people who know how to start up and use the terminal (and, again, are not afraid of it).

BrokenFanControl is DANGEROUS. Changing the maximum fan speed to an inappropriate value may effectively inhibit cooling of the computer. This is dangerous, as it may damage your computer and even set it on fire!

I wrote it because I have problems (broken HD sensor, as said before). It should not be run on a properly working system!

The program was tested only on a Mid-2010 Mac Mini (server edition, the one with 2 disk drives). Should work on any Mac Mini intel but I'm not sure of that. Please do your own testing before installing it!

The script requires python 2.7+ which is the default on both Lion and Mountain Lion, and may be installed on earlier OS X releases.

The code

It is very simple: it just reads, via the smcFanControl command line program, the values of TC0D (the processor temperature) and sets the maximum speed of the fan (F0Mx) also via smcFanControl. The fan speed goes from 1800 when the CPU temp is 50°C or less to the maximum speed when the temp is over 75°C.

The commented print statement are for debug and also use TC0P (probably the CPU heatsink) and F0Ac (the current fan speed).

How to test it without burning your Mac

My code is a simple python script that wraps some call to the command line component of smcFanControl.

Before installing it, test it by uncommenting the print statements and commenting the last subprocess.call call (the one that sets the maximum speed). If the fans start behaving strangely, shut down the computer, wait for a little while and then restart it. Everything should be operating normally.

Installation

The script is installed so that it's called by cron every minute and by SleepWatcher at wake up time (so you don't have to hear full speed fans for a full minute when the mini wakes up).

Follow the instructions. The instructions are not very easy to follow. This is intentional. If you don't understand them, well, you should not use this script. As stated earlier: it's dangerous. :)

• download smcFanControl and install it in /Applications. Beware that you will need version 2.4 and that the script will not work with version 2.5 (or probably later).
• copy BrokenFanControl.py to /usr/local/bin and make it executable
• download SleepWatcher and install it
• • Assuming you've downloaded it in Desktop
• • sudo mkdir -p /usr/local/sbin /usr/local/share/man/man8
• • sudo cp ~/Desktop/sleepwatcher_2.2/sleepwatcher /usr/local/sbin
• • sudo cp ~/Desktop/sleepwatcher_2.2/sleepwatcher.8 /usr/local/share/man/man8
• copy de.bernhard-baehr.sleepwatcher-BrokenFan.plist to /Library/LaunchDaemons
• sudo launchctl load /Library/LaunchDaemons/de.bernhard-baehr.sleepwatcher-BrokenFan.plist
• sudo crontab -e
• • insert the line below (from */1 to end of line)
• • */1 * * * * /usr/local/bin/BrokenFanControl.py
• Enjoy the silence.