The acpifan device driver supports fans possibly exposed by the BIOS. Even if a system contains only one physical fan, multiple acpifan instances may be present. In such cases each acpifan typically represents an acpitz(4) thermal zone, and the combined state of all instances reveals the speed of the fan.
The acpifan driver does not support controlling the fan. The current state (on or off) is made available through the envsys(4) API and the envstat(8) command.