Chosen Solution
I suspect that the SSD temp sensor is bad. I installed this sensor years ago when I replaced the HDD, then later upgraded the HDD to SSD… so maybe the sensor is bad… I’m not sure. I did order a new sensor: OWC In-line Digital Thermal Sensor for 27-inch iMacs (macsales.com) https://eshop.macsales.com/item/OWC/DIDI… I’m hoping it will fix the issue with the fan running at full speed when I power on the iMac. If that does not fix it… I might have to replace the logic board. Not sure what the issue could be.
You may be able to put iStat on there and figure out which sensor is acting up. From there you can formulate a plan to fix. https://bjango.com/mac/istatmenus/
Yeah but iMac won’t even boot up, plus I need to reinstall MacOS on the new SSD
