Chosen Solution
It sounds like the fan on my Mac is going as I can hear the bearings in it grinding. I am trying to confirm (before opening the whole thing up) if this model has only a single fan in it. There appears to only be an “optical drive” fan guide on this site, but when I search online for replacement parts I get results for both an optical drive fan and a cpu fan.
Please check your exact model as this was a transition period and the guides are not there one this model. But Everyman reports that this model is similar to the 2010 model so that guide will probably work: http://www.everymac.com/systems/apple/im… There could be three three. Left, right and a center one behind the logic board. Right optical drive: iMac Intel 27" EMC 2429 Optical Drive Fan Replacement There don’t seem to be guides for the other fan replacements, but you can see the left fans in this guide: iMac Intel 27" EMC 2390 Optical Drive Fan Replacement The center fan requires the logic board to be removed. The guide I am finding is only showing the above guide so I’m not positive because the next model does only have one: iMac Intel 27" EMC 2546 Fan Replacement
