Disabling a broken MacBook fan temporarily to avoid excessive noise

DisableMacFan.sh

# To disable the fan:

# Read the current minimum speed of fan 0, write this down so you can reset it later if you wish to
sudo /Applications/smcFanControl.app/Contents/Resources/smc -r -k F0Mn

# Set the minimum speed of fan 0. To set the min speed for fan 1, replace F0Mn with F1Mn.
sudo /Applications/smcFanControl.app/Contents/Resources/smc -k F0Mn -w 0000

# Set the fan to forced speed mode. The parameter 0001 forces the speed of fan 0. To force fan 1, use 0002. To force both fans use 0003.
sudo /Applications/smcFanControl.app/Contents/Resources/smc -k "FS! " -w 0001

# Set the target speed of fan 0. To set the target speed for fan 1, replace F0Mn with F1Mn.
sudo /Applications/smcFanControl.app/Contents/Resources/smc -k F0Tg -w 0000

# To undo and go back to default speed control:

# Set both fans to automatic mode:
sudo /Applications/smcFanControl.app/Contents/Resources/smc -k "FS! " -w 0000

# Set the minimum speed of fan 0 back to default (1250):
sudo /Applications/smcFanControl.app/Contents/Resources/smc -k F0Mn -w 1388

# To convert normal fan speed values to a format that you can write to the SMC:
python -c "print hex(1250 << 2)"
# Converts the speed of 1250 RPM to 0x1388, use as seen in the command to set the min speed of fan 0 back to default (above).

If you know how, you can put these commands into a .command file and make it executable, so you have a script that you can run from your desktop to manually enable and disable the fans.

Warning: Writing to the SMC directly is risky, and forcing the fan speed down below a limit where it is supposed to be can cause overheating and failure of your computer. Do not do this in a computer which only has one fan!
Disclaimer: I take no responsibility for the safety of your system if you attempt any of this.

Documentation of the tool is available here. Thanks to the author, hholtmann.