Chosen Solution
The display and part of the case was damaged and I mounted it in another cabinet, but now the CPU is at more than 300% of use (kernel_task) so the equipment is very slow, I do not know if I have to do any adaptation or have to do with a temperature sensor.
Sadly, you need the iMac’s display connected, within it are sensors your systems SMC services requires to run. Your system is in CPU safe mode which lowers the CPU’s clocking and ramps up the fan as it is trying to protect the CPU from over heating. The iMac design also leverages the chimney effect in its passive cooling. Basically, the logic board and the power supply need to be held vertically not horizontally as you’ve mounted them. And lastly the case and the display also offer EMI protection as well as a Bluetooth antenna which is behind the Apple logo and along the edge of the display are the WiFi antennas.
