Air Vents
Air vents in the freezer are vital for proper freezer function, including the defrost cycle. If frost is building up in your Samsung freezer, check the air vents. If they are clogged or if their filters are old, air may not be flowing properly in the freezer compartment. Remove any blockages and see whether the frost starts to disappear again.
Defective Thermostat
The defrost cycle is controlled primarily by the thermostat, which uses thermistors to sense the current temperature range of the freezer and initiates both the cooling and defrost cycles accordingly. A malfunctioning thermostat may not allow the defrost cycle to work, or it may not be cooling the freezer properly. You can test thermostat and thermistor connections with an ohmmeter, but make sure you have pinpointed the problem before you try to replace anything.
Timer Problems
Defrost cycles run according to a timer. Once the cooling cycle is finished, defrosting begins. A common problem for defrost cycles is a broken timer. Timers can become stuck and not move onto the defrost cycle even when receiving the proper signals from the thermostat. Failing timers may not work at all, and replacing the timer and its connections can solve this issue.
Defrost Circuit Issues
Sometimes the problem lies within the circuitry the defrost cycle uses to reverse the refrigerant flow and warm the freezer compartment. Components may be functioning correctly, but if you have burnt-out circuits in your Samsung refrigerator, the defrost cycle may not be able to operate. Also, failed circuitry can cause failed fan systems and bad refrigerator pumps, and that can contribute to the defrost issue.