FIXED THE ISSUE.... This took a little time, but it was a simple fix. The LCD sensor that you have to disconnect from before removing the LCD was the issue. After receiving HIGH CPU fan speeds, I began looking at possible issues. First, I had Temperature Monitor Installed. I had all my sensors including the ambient air sensor reading. After I upgraded my HD to a SSD I started getting HIGH CPU fan speeds, but the HD and DVD fan speeds were fine. I looked at my Temperature Monitor and I noticed i had several Temperature Monitors not reading including the ambient Air Temperature (bare with me, these are steps to troubleshoot). After reseting the SMC and PRAM, still nothing. I shut down and disassembled my IMAC again. This time after i removed the LCD, I looked at the LCD cable that you must disconnect when removing the LCD and BAM, I saw the issue. The wires that connect to the Motherboard from the LCD Sensor, inherently like to lay across the screw hole the Bezel attaches to. I have a couple of pinched marked that exposed the wires and when I tighten the bezel down, it shorted the wires and caused the issue. I cut small pieces of electrical tape and covered the bare spots. When I reassembled the IMAC, i mad sure that all my BEZEL screw holes were completely clear of any wires. Once back together, I plugged in the IMAC, waited 5 Seconds and turned it on. All is well. I feel this a majority of everyones issues when they take apart their IMACS and put them back together. Hope this helps.
And, instead of the terrible answer above (which sticks the fans at 1500 regardless how warm the machine is), HDD Fan Control uses the SMART sensors to ramp up the fans when needed.
I really don't understand why this program is never mentioned when someone brings up the fan problem when you change a hard drive in an iMac... but there you go."
Same thing here. All fans are now continually going crazy. Everything is connected fine. I don't get it. An SMC reset doesn't work. PRAM doesn't help. Makes no sense for all the fans to be going nuts. I wonder if it is related to the LCD temp sensor. I wonder if that could be making the fans ALL continually run.
