Also, if you have the original install discs that came with the iMac, you can run the Apple Hardware Test. You will need to restart the iMac and hold down the Option key whilst restarting. You soon see a violet or blue background with straight and curved arrows. Look for a button/icon to pop up labeled "Apple Hardware Test", click on it and click on the straight arrow. This will boot the iMac off of the CD/DVD disc and into AHT. There will be several tests to pick from, but there should be one for the cooling fan controls. Run that along with the CPU calibration tests.

73s de Phreakout. :rambo: