List the directory.
If you have ACPI support you should have a directory under /proc/acpi/thermal_zone and some directories under /proc/acpi/fan
evo acpi # ls -R /proc/acpi/fan
C1F6 C1F7 C1F8
My Laptop also has three fan states
The fastest fan state happens to be C1F6
evo acpi # echo 0 > /proc/acpi/fan/C1f6/state