Quote Originally Posted by rejieah View Post
mga bro, ok lang ba umikot agad ang fan sa may radiator kahit naka-on pa lang ung susi, di pa man kac ako nag-start ng engine umiikot na yung fan, kahit sa umaga. Thanks!!!
Thermo fans run on a temperature sensor normally located in the coolant piping somewhere. If the sensor is faulty the fans will come on when the ignition is on. The fans will also consume power from the engine all the time making it less fuel efficient.
If the car overheats at speed, the problem is either a dirty/clogged coolant system or the radiator is incapable of handling the cooling (too small).

Or.

If ignition is on fan will come's on when the system is in the defrost position (on not off position), the AC compressor runs to help dehumidify the air being blown on the windscreen to more quicly clear any mist. Whenever the AC compressor runs, the condenser fan (and somethings the regular cooling fan as well) will turn on to maintain airflow over the condenser.