Samsung RS20

[helen74]

the appliance appears to be working when 1st switched on, the fridge&freezer both cool down to normal temp, it seems to run for a day ok, and then it just defrosts, and loses its temp and the appliance doesnt come on till its switched off at the wall and then back on and it will work again for another day. Its as if once the compressor shuts off it forgets to come back on.

[platinumfreeze]

Try tying a string around one of the compressor tubes to remind it to come on.

[tonto33]

thermo fuse faulty, had few of these tried changing defrost sensor and heater still made no difference till changed fuse and it worked and never been recalled back to one

[paul_h]

As tonto33 says, more than likely the thermal fuse.
What is happening is that everytime it tries to defrost, it loses the plot since there's no path through the defrost circuit.
It could be the heater itself, or just a dodgey thermal fuse.

edit: I did have one that had a faulty relay on the PCB though. But the fact it works when you reset the mains power points to a defrost error. You'll have to rip the evap cover off and check the heater resistance with a multimeter before you can be fully confident it's only the thermal fuse.
Also some times the fuse blows because the the defrost thermistor doesn't terminate (read the right voltage at warm temps)

Has the temp display ever flashed?
That's a good indicator the heater or thermal fuse is open circuit.