I've just installed a new SSD in my mid 2010 27" iMac. I put it in place of the disk drive (ODD) so now there is no optical disc drive in my computer. After I did the installation I noticed that the fan speed shot up to ~3000 rpm and stayed there. So I downloaded SSD Fan Control and I'm currently using it to keep my ODD fan speed at ~1000 rpm. The system is running fine (from what I can see) and the noise it down to a minimum.
What I want to know is are there any dangers in doing this? The SSD isn't going to generate much heat at all but if there anything else around that part of the iMac that will generate enough heat to warrant letting the machine set the fan speed?
I'm assuming that this change in fan speed has happened because there isn't a signal being sent to the ODD temp input in the machine (since I've taken the ODD and thus the thermometer out, so it's defaulting to the highest rpm possible.