FAN is running at high speed when off or in sleep mode.
A problem with a 2012 21,5” iMac. If it’s off or in sleep mode the fan is spinning at high speed. iMac is working quite well, even the fan doesn't behave strange as along as the computer is running. But it becomes strange when I shut down (or sleep mode) the Mac, because when the machine is OFF, the fan runs riot.
The fan stops only in this two cases:
- I physically disconnect the power cable. After doing so, I can wait as long as I want (I tried 8 hours during night). In the very moment when I reconnect the power supply, the fan instantly starts running at top speed and won't stop again (I lost patience after 20 minutes and then I pulled out the plug again).
- I press the on/off-button on the back of the lower left corner of the Mac. In this case the fan stops on the spot and the startup-procedure beginns and everything is fine.
Tried all the SMC and NVRAM resets and disconnected the harddrive when it was open, but nothing helps.
Does anyone know what this problem is? Maybe a faulty sensor on the logicboard?