Ender 3 Pro weird reverse thermal runaway

[airscapes]

2 things;
PETG should need NO Cooling fan. Only time it is needed is if you are printing something tall and very thin.
If you place a hot end you need to run a PID on it so it will maintain the proper temp. This calibrates how the main board controls the power to the heater.
I can not tell you how to do it on your machine. Google your model and "Performing a PID calibrations "
Good luck

[dpc166]

2 things;
PETG should need NO Cooling fan. Only time it is needed is if you are printing something tall and very thin.
If you place a hot end you need to run a PID on it so it will maintain the proper temp. This calibrates how the main board controls the power to the heater.
I can not tell you how to do it on your machine. Google your model and "Performing a PID calibrations "
Good luck

Thanks! Did not know that you didn't need the cooling fan for PETG and when I replace with the sprite pro direct drive extruder next weekend, I'll certainly run all of the updates and calibrations I need.