imac 21 inch mid 2011

[andrespi]

This equipment has a problem that occasionally turns a lot of fan without demanding a lot from the machine.I have done test apple service diagnostic but it does not report failure.
I don't know if it's a fan or overheating problem, maintenance or problem on logic board

 

[2informaticos]

Install HWMonitor and check the temps when fan goes high.

Test it with USB macOS, to discard software issue.