Do not run the head without the fan. Not a good idea at all. Those halogen lamps run very hot. On the D series Chromega II heads you'll have several problems, and I'm sure the C series dichro heads are the same. First the lamp's life will be shortened considerably. The light mixing box will run too hot and the extra heat will degrade the foam liner more quickly. The foam liner is nothing but white styrofoam, and doesn't tolerate heat very well. First it will turn yellow/brown, then it will melt. Oh, did I mention that you'll smell it getting hot? Trust me, you will. Ask me how I know this. I've had to re-line my mixing box.