Please be more specific. What kind of car, what year model, engine size. The more information you can give us about your vehicle the more likely we will be able to help!
HVAC fan? Engine cooling fan?
If the AC or Defroster is on, many vehicles will also turn on the cooling fan.
get in the car when it is cold, turn on the ac, then check under the hood. the fan that is not spinning when the car is cold is the cooling fan
196-203
temperature sensor is bad
Check the thermal relay for the cooling fan.
Check the fuses, check the relay and then check the fan motor.
You got to first plug it in and second turn it on
The passenger side cooling fan comes on when Air Conditioning is turned on. If it still does not turn on, check the AC fuse and the AC/Fan relay.
check the coolant temp. sensor, this sends info to the computer to turn on the cooling fan. Check for other answers for the cooling fan, I posed a answer on how to replace the fan relay with out removing the front facia and bumper
There is no fan control switch, and no direct connection to any sensor or switch on that vehicle. The system works like this. The computer(PCM) decides when to turn on the fan. The PCM looks at engine temperature from the ECT sensor, and AC input from the AC control head switches. When the PCM decides that you need the cooling fan to come on, it uses the cooling fan relay, and the cooling fan high speed relay to turn on the fan, and whether it should run at low speed, or high speed. The power input to the cooling fan comes from the cooling fan relays.
Perhaps there is no problem at all with your car's cooling system! The fan(s) you observe are controlled electrically by a second engine thermostat which will turn the fan on only to support cooloing when there is little forward motion of the vehicle. The fan(s)are designed to turn freely in the rushing wind and will only turn on when your car slows and needs "wind" to continue the cooling.