Manually turn on CPU fan

Solution 1:

You can do this with the tool

pwmconfig

This tool is normally used to save a configuration file for fancontrol. But you don't have to do so. You can just start the tool, than it will put all fans on full speed, sowing there current speed like this:

Giving the fans some time to reach full speed...
Found the following fan sensors:
  hwmon0/device/fan1_input     current speed: 2129 RPM
  hwmon0/device/fan2_input     current speed: 1679 RPM
  hwmon0/device/fan3_input     current speed: 0 ... skipping!
  hwmon0/device/fan4_input     current speed: 0 ... skipping!

After that you just skip (Ctr+C) the tool without saving anything.

To install the tool, you can use the following command:

sudo apt-get install fancontrol