Once the cooler is installed, plug the CPU fan connector into its header on the motherboard.
Once the cooler is installed, plug the CPU fan connector into its header on the motherboard. This is usually somewhere close to the CPU socket and labeled something like "CPU_FAN." If you have a larger cooler with two fans, you'll also need to plug in the second fan (usually on a nearby header labeled "CPU_AUX." And if you're installing a liquid AIO cooler, the pump also needs to get plugged in, with many boards offering a "CPU_PUMP" header connector as well.