fan runs constantly?

You can try resetting the SMC, disconnect the power adapter and battery and hold the power button for 5 seconds to reset. Reconnect your power and boot.

If you still have the problem:

Your fans are always running, you just shouldn't hear them most of the time because they're running at a low RPM. The fan speed is based on temp. sensors and they speed up when things get warm. For safety, if one of those temp sensors fails or the cable comes loose, the fan will run at full speed right from turning on (assuming already "cold"). The apple store or service center can diagnose faulty temp sensors and runaway fans if this is the case. The temp. sensor parts are usually pretty cheap but there's always a possibility something else isn't working correctly.

 

2000rpm for both fans is the normal idle setting.

 

On the white macbooks its at 1800 rpm. My base is around 2300 rpm set with FanControl because it got way too hot.

 

Try using iStat to check your CPU temperature. If there isn't a CPU field, then you sensor failed, like in my case. Fans will never go off of the max, there are ways to limit the max fan speed. I'm out of warranty, so I did that.

 

I use smcfancontrol to control my fans. 2000rpm is the base speed. I usually run mine at 4000rpm, and that keeps it mighty cool