I recently got a 2003 mazda 6S and found the passenger side radiator fan not plugged in but the car doesn't overheat, and the AC works OK with it not plugged in. When I plugged it in, it runs when the car starts but sounds noisy. Can anyone tell me when these fans should run and if the fan noise is normal?

 

The cooling fans should kick in in two conditions , when the engine is at operating temperature the cooling fan will kick in . When you turn the A/C on the other fan kicks in but cuts off after a few seconds approx 20 secs, Get someone to press the A/C button and observe which fan starts up as you press the switch , this will indicate which fan is the cooling fan and which fan is the A/C condensor cooling fan. If it noisy , Extreamly noisy get it replaced