hi welcome to the abstract world of Samsung fridge freezers.
If the machine is still under warranty then call them out again, tell them whats happened.
Between you and i what probably has happened is that the evaporation cover (bottom inside of fridge side) has become saturated over time (Samsung are aware of this) and when the machine runs its own defrost programme it fails to pick up the fact that the insulation is sopping wet, thinks its finished defrost and resumes chilling, the water in the insulation then re- freezes causes the cooling fan to ice up this then causes repeats of the problem you have.
Have you noticed a noise from inside fridge that stops when door is opened, Thats the plastic cooling fan rubbing the ice forming behind the evaporation cover.
Samsung have made alterations to this cover better air flow etc and waterproofed the insulation.
When you speak to warranty people tell them your aware of the problems with cover and icing it may cut down on the time they take to resolve your problem.
hope this helps.
oh and you might want to tell them to change the defrost term sensor too!
grumplin, July 2006