On any computer, and Mac's aren't an exception, you can't control how its fans work as they are controlled by the CPU depending on the workload and the temperature reached by the computer. That's why you've probably noticed that it overheats and that's due to the fact that the system doesn't consider that it needs to cool down.
How to adjust the speed of your Mac's fans
Well, you can control it and establish a minimum speed to make the temperature drop thanks to an app called smcFanControl for Mac, that comes along with excellent options and that you can run on different versions of macOS, including El Capitan or Sierra.
Control when your computer should cool down.
This tool offers you the possibility to control the fans of your Mac but without any risk for your computer as it doesn't wipe out the default settings to make sure that the fans are activated with the CPU needs them. These are the functions included in the program:
- Customized settings for your Mac's fans.
- Shows the temperature and speed of the fan on the menu's bar.
- Establish minimum speeds for each fan separately.
- Adaptable to the power source used.
Using it is very simple but you have to bear in mind a few precautions to be taken into account, as you need to have certain knowledge in this field before you start mucking around... However, remember that it can only be used with Intel processors.