OS X's fan speed control

[JohnonMac]

My system is working almost 100%, only two issues left: fan speed and Teamviewer (i'll ask that in a separate thread to keep things apart).
I have a case fan connected to the SYS_FAN1 connector of my mobo. In BIOS I've set the 1st/2nd/3rd System Fan Speed Control to 'Silent'. Under Windows this works beautifully, the case fan runs at low speed and is very silent. In OS X ML however the fan speed leads it's own life. Sometimes it runs at low speed and is silent and sometimes it runs at high speed and is loud. There does not seems to be a relation with the temperature of the CPU Cores, CPU Heatsink, Northbridge or harddrives, the fan speed jumps randomly from low speed to high speed and back. I know there is no application to control the fan speed, but is there a way to influence OS X's fan speed control? Or to disable it altogether, so the speed is controlled by the BIOS (like under Windows)?

System info:
Bios version: F14
OS X ML 10.8.2 with Supplemental Updates
Power Management working

 

[JohnonMac]

Anyone please?

 

[Dschijn]

How many pins does that fan have? 3pins or 4pins?

 

[JohnonMac]

How many pins does that fan have? 3pins or 4pins?

It has 3 pins. It is connected to SYS_FAN1 (see image), the speed is controlled via voltage regulation. Pin 4 (VCC) is not connected. Should I use a fan with a 4 pins connector and connect it to SYS_FAN2 or SYS_FAN3, so the speed is regulated via PWM? Is that how OS X's fan control works? (For example this fan? "The NF-S12A PWM sports Noctua's custom designed NE-FD1 IC for fully automatic speed control via 4-pin fan headers and comes with a Low-Noise-Adaptor to reduce the maximum speed during PWM control from 1200 to 900 rpm.")

 

[Solidww]

It has 3 pins. It is connected to SYS_FAN1 (see image), the speed is controlled via voltage regulation. Pin 4 (VCC) is not connected. Should I use a fan with a 4 pins connector and connect it to SYS_FAN2 or SYS_FAN3, so the speed is regulated via PWM? Is that how OS X's fan control works? (For example this fan? "The NF-S12A PWM sports Noctua's custom designed NE-FD1 IC for fully automatic speed control via 4-pin fan headers and comes with a Low-Noise-Adaptor to reduce the maximum speed during PWM control from 1200 to 900 rpm.")

Have you set the fan control as PWM in your BIOS? When I do a task that loads the CPU the fans do speed up a little bit on the current builds. They don't scream up though. Usually, only a few RPMs. Is that enough for your needs?

 

[JohnonMac]

Have you set the fan control as PWM in your BIOS? When I do a task that loads the CPU the fans do speed up a little bit on the current builds. They don't scream up though. Usually, only a few RPMs. Is that enough for your needs?

Yes, a few RPMs more would be fine. The BIOS has these settings for the system fans:

-------------------------------------------------------------
1st/2nd/3rd System Fan Speed Control
Allows you to determine whether to enable the system fan speed control function and adjust the fan speed.
- Normal: Allows the system fans to run at different speeds according to the system temperature. You can adjust the fan speed with EasyTune based on your system requirements. (Default)
- Silent: Allows the system fan to run at slow speeds.
- Manual: Allows you to control the system fan speed under the Slope PWM item.
- Disabled: Allows the system fan to run at full speeds.

Slope PWM
Allows you to control the system fan speed. This item is configurable only when 1st/2nd/3rd System Fan Speed Control is set to Manual. Options are: 0.75 PWM value /oC ~ 2.50 PWM value /oC.
------------------------------------------------------------

I have currently set 1st/2nd/3rd System Fan Speed Control to Silent. I have also tried Manual and set Slope PWM to 0.75 PWM value /oC, but that also doesn't work under OS X. Nor does setting Normal. OS X ML seems to ignore the BIOS settings. Maybe I should buy a 4-pin fan that has speed control via PWM.

 

[GP-SE]

try using "normal" and see if that helps.

 

[JohnonMac]

try using "normal" and see if that helps.

Thanks for your reaction, but I already tried that, see my post above: "I have also tried Manual and set Slope PWM to 0.75 PWM value /oC, but that also doesn't work under OS X. Nor does setting Normal."

 

[ffk]

I believe you need a 4 wire fan to use PWM.

 

[JohnonMac]

I believe you need a 4 wire fan to use PWM.

I think you're right, after reading the reactions and thinking a bit more about it. I'll buy a new case fan, probably the one I mentioned in post #4, when it's available in the shops (it's brand new, just announced yesterday).

Thanks everyone. If someone has a definitive answer on how OS X's fan speed control works (4 pins with PWM? Does it obey the BIOS settings?), please chime in.