There is a jumper switch like those that you would find on a pc motherboard. It is located on the smaller circut board that has the on/off switch on it. When the jumper is closed, the fan will run all the time while on heat and it will shut off while on cool. Taking the jumper switch off (open circut) will reverse this. Off while on heat and continous run on cool. You will need to switch it back in the summer. My unit has an adheasive sticker that I took off of the plastic cover next to the on/off switch that reveals this jumper. With a set of tweasers it can be easily changed. Now if you could go to Radio Shack and find the parts to create an on off switch to wire into the two jumper pins you could control the fan setting much simpler.