For acerhdf, add a line to /etc/modprobe.d/options.conf like this:
This will log the temperature every 10 seconds (to /var/log/syslog IIRC) - and it lets you control when the fan comes on or goes off. When you're happy it's working, set verbose=0 to cut out the log abuse.Code:options acerhdf verbose=1 fanon=62 fanoff=52 interval=10
These are the temp settings I am using. It gets a little warm but doesn't run the fan constantly.