After contacting the acerhdf author a solution was found.
It looks like that on Ubuntu 10.4 the /etc/modprobe.d/acerhdf.conf is not correctly read when loading the acerhdf module.
When after booting the module is removed and reloaded with: modprobe acerhdf kernelmode=1 the module
works correctly *and* is using the fanon/off parameters given in the acerhdf.conf file.
After contacting the acerhdf author a solution was found.
It looks like that on Ubuntu 10.4 the /etc/modprobe. d/acerhdf. conf is not correctly read when loading the acerhdf module.
When after booting the module is removed and reloaded with: modprobe acerhdf kernelmode=1 the module
works correctly *and* is using the fanon/off parameters given in the acerhdf.conf file.