This is an interesting problem. My fan clutch only operates intermittantly. It seems that most of the time it doesn't engage when the air conditioning is turned on. Turning the air con off then waiting a bit seems to fix the problem. It also doesn't seem to engage at idle speeds. It only engages around 1300 RPM or so. I don't know if that's normal or not. When it does engage, it works perfectly. Is the clutch itself broken or is there something else at fault here?