high cooling fan doesn't work

My son has a 2000 ford focus and the high cooling fan only works when the AC is on. When the Ac is off any low or high velocity is reached at the twin fans. we replaced the temperature head sensor and the fans control resistor and it still does't work.

You mean the cooling fan at the radiator or the blower inside the car? The cooling fan at the radiator usually doesn't start it's operation until your gauge reads 30% higher from the Normal range. You replaced the sensor on the head? There are 2 sensors, one for the cooling fan (2 wires) and one for the computer (3 wires). The high and low fans have their own relay inside the CCRM (constant control relay module). It is on the drivers side of the car under the intake plumbing. Close to the strut tower. It may be bad. Go to the boneyard to get a used part. It is expensive from the dealer. You should be able to get one for about $30 which is only 10% of what a new part would cost.