it could be the defrost timer, some of these have an inbuilt fan delay. either that or you have one of those supco timers that are electronic, worked via cpacitor / resistor. saw this before with one. would go on a defrost every 4 - 5 days and stay on for hours. supposed to be 4 times a day for around 15 mins.
i do this for a living and i would never buy a frost free!!
fridgy phillip, June 2005