Chosen Solution
Hi I have an issue with my iMac. The fans kick in from boot up (even before the log on screen sometimes) and run at what sounds like 100%. Macs fan control shows CPU fan at 3900 and ODD at 3500. The only temp that looks strange is the LCD proximity one - 49-55C. Any idea what the issue is? The apple hardware test reported no issues. I have done a fresh install of OSX.
If you are hearing fans speed up right away it is definitely that LCD temperature sensor cable. If you have the tools, I would pull up a repair guide and see if you can’t adjust that cable. A cheap and easy possible solution would be to replace it.
