* The fan is controlled by the AC pressure switch. When the AC is turned on, the pressure switch sends a signal to the fan control module, which turns on the fan. When the AC is turned off, the pressure switch opens and the fan turns off.
* The fan is wired incorrectly. The fan may be wired so that it only receives power when the AC is turned on. This could be a mistake made during a repair or installation, or it could be a factory defect.
* The fan motor or relay is faulty. If the fan motor or relay is faulty, the fan will not turn on even when the AC is turned on.
To determine the cause of the problem, you will need to test the fan, the pressure switch, and the wiring. If you are not comfortable doing this yourself, you can take your car to a mechanic for diagnosis and repair.
