I had LMDE installed about a year and it worked really great OOB! But as I reinstalled the system this coolerproblem appeared! The cooler just would not be regulated accordingly to the temperature.

Reinstalled the Distribution after some time using Katya.
sudo aptitude update
sudo dist-upgrade -f -y
now the coolers working again.

I guess there was an error during the installation
or some bug which broke the cooler driver or something
in that direction