Which fan header should I use?
A 4-pin fan connection should always be used with PWM coolers. It does not matter which fan connection is selected. Either "CPU_FAN" or "CPU_OPT" are recommended. With the Liquid Freezer II, connection to a pump header leads to a permanent, unregulated speed of 100%.https://www.arctic.ac/en/CPU-Cooler/Which-fan-header-should-I-use