I have this MacBook Air that has been having a fan problem over the past few weeks. The fans run at full speed ALWAYS. As soon as you hit the power button, before the system even starts booting, the fans rev up to full speed. And they don't stop until you shut down.
According to SMCFanControl, the fans are running at 7600 RPM even though their max RPM is 6500. I expect the fans going to wear out soon at that high speed.
Also according to Hardware Monitor.app, all of the temperature sensors are returning reasonable values. The CPU is about 150°F and thats the hottest, everything else is much lower. So the fan speed doesn't seem to be reacting to a temperature issue.
Reset the PRAM to no effect.
Checked Activity Monitor but even when fully idle, the fan just revs away.
Ran an Apple Hardware test, it returned that there might be a problem with the fan, but gave no other details, other than 'bring it to apple'.
To me, it seems like its probably a logic board problem, as a fan probably wouldn't make the fan rev UP? And none of the normal causes for fans to rev up seem to be causing this fan to rev up.
I did not try one of the fan utilities that let you set the actual speed, not just the minimum speed. I'll have to try this next. I also realize I didn't reset the SMC, I thought I did but on this Mac, a different process does that. I wouldn't be surprised if that fixes it. But I'm going to submit this question anyway in case anyone else have some insight.