the freezer randomley part /fully defrosts it usualy runs on setting 3 as dose the fridge.
i have cleaned all grills and vents the last time this happend was 2 months ago and blamed the children for not closing the door tight and after a short time [1] day of being turned off it began to work fine but now there seems to be no consistancey with freezing it has a joint of beef in at the moment whitch has just stayed frozen but bread /icecream keeps defrosting it seams to be running as it should turning on and off freezing ice but then it part melts it produces cold mist now and again as it allways has i hope there is enough info for you and hopfully its somthing simple to fix

paul, January 2015