Prusa i3 Auto Cooling not fun-fan ....

Done some 10 prints testing print dize.
I only get printing finish if I turn off Auto cool in slicer setup
When it's on with default values after 2 first layers fan turns on and Extruder temp goes slowly down from 245 C until printing craps out like when Xtruder temp is coming down to 200-210
Plastic does not attach any more.
How is this cooling supposed to work ? Is that correct behaviour that it shall slowly go down from 245 (each layer)
Printing e.g. dize 17x17 mm
Guess I need Auto cooling on ?? Since when I turn it off I don't get totally good result, even though I get the whole dize printed ...
Just the basics what to expect from Auto cooling feature would be nice if someone can explain.
Also my heated bed goes down from 110 to like 85 when half job done and printing craps out. Should that also decrease ... ??
Thanks
Ha det gött
Bosse

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Prusa i3 Reworked, Delivered March 28 2014, RAMPS 1.4
Göteborg, Sweden

What is "dize"?
Print temp should remain around 245 if that's what you have set. It sounds like your cooling fan is blowing on the hot-end causing it to cool too much. You should either insulate your hot end, or direct the fan onto the part more, away from the heater.

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Waitaki 3D Printer

Thanks for info Waitaki. That was very useful learning for me.
Even though it seems pretty obvious, when you tell me, I wasn't totally clear on that fan is only to cool printed part, NOT extruder head
I'll go check out that new learning now
Ha det gött
Bosse

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Prusa i3 Reworked, Delivered March 28 2014, RAMPS 1.4
Göteborg, Sweden