[SOLVED] Gigabyte X399 Designare EX motherboard - Documentation unclear for which fan connector to use for liquid cooler

[robert_e_bone]

So, I have a Gigabyte X399 Designare Ex motherboard, new, and I have an Arctic Liquid Freezer 120 cooling system. It is not clear which fan connector I should connect the cooler to. Normally, the CPU_FAN connector would be used for cooling the CPU, but I also see 2 other connectors next to that - , CPU_OPT, and SYS_FAN6_PUMP. It would seem logical to me that since I am using a CPU cooler - which is the combo of a fan and a pump and a radiator with enclosed fluid, to use the SYS_FAN6_PUMP connector, however, I have seen doc in the past that says to use the CPU_FAN connector for cooling the CPU. That doc also indicated some systems would not boot if they did not detect an above zero RPM reading on the CPU_FAN connector, which would be the case if I plugged the cooler into the SYS_FAN6_PUMP connector.

I REALLY do not want to get this wrong, so anybody who can give me guidance, THANKS

 

[robert_e_bone]

Well - as far as I can tell, deeper into the manual for the motherboard, it seems that while there 2 headers for SYS_FAN5_PUMP and SYS_FAN6_PUMP for presumably dual video card liquid coolers, that the CPU_OPT header seems to be the one to use for a liquid cooler for the CPU, and here is pretty much all the doc says about its purpose (the rest of any doc on it talks about the pins and a foolproof connector design): "CPU_OPT (Water Cooling CPU Fan Header)". SO, this appears to be the one. I had missed seeing that in the manual earlier, prior to my post of the thread, and I apologize for that.

 

[Paperdoc]

From the manual for that Artcic Liquid Freezer 120 AIO system, it appears there is only one electrical connection to be made. It supplies power and control for both of the rad fans plus the pump unit. That is somewhat interesting because, like any fan header, the mobo CPU_FAN header can only deal with a speed signal from ONE device, so only one of those three items can have its speed sent to the header.

A CPU_FAN header has THREE important functions:

1. Provide power to the CPU cooler - in this case, to all three components.
2. Provide control of cooling of the CPU, based on actual temperature measured by a sensor built onto the CPU chip and fed out on one of its pins. MANY AIO systems do this by varying only the speed of the FANS on the radiator, and keeping the speed of the PUMP constant at full speed.
3. Monitor the cooler for FAILURE - that is, NO speed signal coming back to it. If failure happens, it sends out a fast warning and many mobos will shut down the system rather quickly without even waiting for the CPU temp sensor to detect high temps.

For item 3 above - FAILURE detection - you should ensure that your actual CPU cooler is connected to the CPU_FAN header, becasue that's the only one that does this job. It MAY be designed not to allow you to start up if it gets no immediate speed signal. There is no other connection to be made to any other fan header as far as the CPU cooling system is concerned. Of course, you do need to connect case ventilation fans to your SYS_FAN headers.

The Arctic website does not tell you which of those three components (the pump or one of the two fans) feeds its speed back to the mobo fan header. My speculation is that they have it send back the PUMP speed, because that is the most critical of those three for failure events. If they have done that, then you will never "see" anywhere the speed of the rad fans, because there is no mobo connection to read them.

Just so you understand, I am sure they have used a little quirk of fan designs in this system. The FANS of that AIO system are of the 4-pin PWM design and need to have their header set to use the PWM Mode in BIOS Setup. That way the header can control their speeds. The PUMP unit, however, is shown with only three wires going to it, just like a 3-pin fan. Such a unit, connected to a header using the new PWM Mode, can only run full speed - no control. BUT as I said, most AIO systems WANT the fan to run full speed all the time, so that's what this will do. And IF the design has that PUMP speed as the one item sent back to the CPU_FAN header, then you will see it constantly at one speed, with only tiny changes. None of this causes any problem with ability to CONTROL the speed of the two rad fans. It only means their speeds will not be displayed anywhere.