Fan is on all the time
I have read similar threads here but not exactly this one. I had my MacBook Pro 2.4Ghz for motherboard repair. When I got it back the fan is an all the time, even when the MB is cold. I have done the SMC reset, PRAM reset etc. with no help. I ran iStat Pro and it says that left fan is 0 rpm and right fan is 2000 rpm. So I opened up the MacBook and I see that the left fan is the one really blowing away while the right fan is moving much quieter. The CPU load is low and the temps are low. I read about someone suggesting a sensor might be disconnected and that could be the reason iStat does not see a left fan even though it is blowing like crazy. Does anyone have a link to where I can check if this sensor is not correctly in place after the repair? Just to make sure I am testing with 85W power.
Here is what I did. I opened the MacBook Pro and removed the left fan cable. Careful, careful, the correct way to remove these contacts is to gently pry with a spudger (Spudger) or similar and gently pull upwards. Look carefully for the text "Push" on top of the contact. I know because I have done my mistakes on these cables through the years :-(
I inspected the cable and made sure they were well seated into the contact. Put the fan cable back in place and now both fans are visible in iStat. So it must have been one of the 4 cables to the contact that has come loose when the fan was put back. Horray! MacBook Pro 2.4Ghz with 256MB vram ATI8600M (not bad really!) working for me again :-)
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I'd put it back in the hands of whoever "fixed" the machine and have them deal with it. It's not right that you should be stuck with this issue after paying for a repair, and not only that, but if you modify it further, you might void your warranty with the person/company if there is one.
I'd remove extended memory and battery while testing, and make sure you're using an 85W AC adapter (Pros can have problems with 60W adapters that are meant for MacBooks).
You could try to determine if a fan is defective by swapping the fans and seeing if the behavior changes, i.e. if the "good" fan starts behaving the same way the "bad" one does. The fans may not fit in the opposite spots, but you could test them with the topcase loose, and without fully seating the fans in their positions. If the "good" fan behaves and is not on high while in the opposite spot, it may be that the "bad" fan is in fact "bad", and needs replacement. And if the "good" fan behaves like the "bad" one, then likely the fans are fine and you're dealing with some other issue.
I'd also recommend blowing out the fans and everything under the topcase with canned air. Sometimes dust in the wrong places can cause problems, and things do tend to get shifted around when a repair occurs.