Hi.
This is the international section.
We speak English over here.
That fan has a yellow wire.
The yellow wire usually has the speed feedback signal, so the speed can be monitored.
This also means that there is a piece of electronics inside your fan.
That piece regulates the motor, and creates the feedback signal.
That again means you cannot control the fan speed via some external signal.
Fans that can do this have a 4th. control wire.
Of course you need to find the datasheet of that Forcecon fan, so you might find out whether you can hack it to do different speeds reliably.