[SOLVED] Exhaust fan at constant high RPM?

[cmabalot2000]

So on an old rig the exhaust fan is running at constant high RPM and its noisy and annoying. The CPU idle is running at 70 so im getting a new cpu cooler and reapplying thermal paste to try fix that temp problem.

Will this fix the problem, if not, what temps are the chassis fans dependant on.

 

[Paperdoc]

The CPU_FAN header (and any associated like CPU_OPT) are controlled based on the temp sensor inside the CPU chip. The SYS_FAN or CHA_FAN headers should base their control on a different sensor on the mobo. But various mobo makers have allowed other options to be chosen in BIOS Setup where you configure each of those headers separately. The mobo sensor normally is offered, and some also let you choose the CPU internal sensor; some even make that CPU sensor the default setting for the SYS_FAN or CHA_FAN headers, but that's a poor choice. The main reason for that option, though, is the situation where you do need to control a fan according to the CPU temp, like if it is used for fans on the rad of an AIO cooler system.

Some mobos include additional temp sensors on specific mobo components like the North Bridge, the Voltage Regulators, etc. These are used only when you arrange a fan specifically to cool that item and want to control that fan for that area only.

Aside from choice of temperature sensor, here are other items to check for.

1. Is that fan actually plugged into a mobo fan header? Or perhaps, into an adapter that connects directly to a PSU power output. No speed control is possible in the latter case. Another possibility for fans supplied with a case is that it is conneted to a "controller" built into the case which may simply be a switch to choose manually from a limited range of speed settings.
2. Which type of fan is it? That is, 3-pin or 4-pin. The two types have connectors that allow you to connect any fan to either type of header. But in the specific mis-match case of a 3-pin fan plugged into a 4-pin header using PWM Mode, you have no speed control.
3. In the configuration of the header, what is its MODE setting? For some time now, all mobo fan headers are the 4-pin type. But that does NOT tell you what control signal system it is using, and often you have options to set this Mode parameter. Those may include Auto (supposed to test the fan and decide on its own which way to go), Voltage Control Mode (aka DC Mode) that is the ONLY way to control a 3-pin fan, or PWM (the new mode ideal for 4-pin fans). Some fan headers have NO options, and always do one of these Modes. It can be hard to tell sometimes what capabilities a fan header has. But as an example, IF this is a 3-pin fan and IF its mobo header is set to PWM Mode or IF that header can ONLY use PWM Mode, then it cannot control that fan's speed.
4. Also in the configuration options, what control Profile is set? That is, what kind of control strategy is being used to decide what the signal to the fan should call for? Options often include Standard or Auto or some such that uses a pre-set "curve" of fan speed to run for a set of temperatures at the relevant sensor, Turbo for constant full speed, Quiet for constant low speed, and Manual or Custom, which is a variation of automatic control that allows you to set your own "curve".

IF your fan is connected to a fan HUB and IF it is a 3-pin fan, it is very likely that the Hub can only operate in the new PWM Mode and cannot control the speed of that 3-pin fan.