He's partly right. Turning on the AC automatically turns on the fan, no matter what. But, there is a temperature sensor in the engine or head mounted on the side or top that detects how hot the engine is running. This sends a signal to the computer which determines whether the fan is required to cool the engine coolant.

Answered by rivermikerat (expert)
5,494 answers provided

And it sounds like the AC needs to be recharged.

Answered by rivermikerat (expert)
5,494 answers provided

thanks for the response sir..

i compare my chevy optra to other car when the AC is off. even my engine is to hot still my fan not working but other one works.. do you think sir my temperature sensor is not working?

Response from rochjohn19
6 questions asked

It's either the temperature sensor, the fan relay, the fan fuse, or the fan. See if the fan has power. If yes, replace it. If no, trace the wire back to the next location (temp sensor or fan relay). See if there is power. Keep going until you find the faulty part.

Answered by rivermikerat (expert)
5,494 answers provided

only if the AC is on the fan has power, but when the AC is off it will not work.. how do i check sir if there is a power? yes sir i will check all that posible problem.. i will comeback to you sir.. thanks..

Response from rochjohn19
6 questions asked

one thing sir.. is it okay if i direct the power of fan when i start the engine? i mean everytime that the AC is off the fan is always on..

Response from rochjohn19
6 questions asked

It sounds like the temperature sensor is bad. If the AC turns the fan on, most likely the fan relay is good. If you have a meter or test light, get the car up to operating temperature and see if there is power to and from the temperature sensor. You car isn't available in the US, so I can only guess at its location. It'll be somewhere on the head or the engine block, probably in front.

Answered by rivermikerat (expert)
5,494 answers provided