There are 3 main types of defrosts

1. mechanical defrost timer (this is normally set to a time period. Example every 12 hours a defrost will take place for 15 minutes)
2. pcb type set on a variation between temperature of evaporator (matrix) and compressor run time.
3. pcb thats sets defrost only on run time of compressor.

What The Automatic Defrost Cycle Does on this Samsung fridge freezer
Automatic Defrost Cycle

In units with multiple evaporators, automatic defrost operates on both evaporators individually. An evaporator has a heating element that melts any accumulated frost or ice. Thermal sensors located around the evaporators send information to the main processor. This information determines when the heater will begin defrosting the evaporator.

After the initial power up, the first defrost cycle normally occurs after 4 hours of compressor run time. After that, the minimum and maximum times between cycles is 6 to 11 hours for the refrigerator and 12 to 22 hours for the freezer, respectively, for single evaporator models. For dual evaporator models with Twin Cooling, the intervals are 6 to 8 hours for the refrigerator and 12 to 16 hours for the freezer.

Thermal fuse can be checked using continuity with a multimeter. 

Ntc sensors can be checked using ohlms with a multimeter. 

The sensor has a reference impedance of 5K Ohms at 25C. Impedance goes up when temperature goes down. At room temperature the sensor should show between 4 and ten Ohms. The chart below shows impedance values for the 502AT in function of temperature (in the middle column).

The defrost heating elements can be checked using ohm's law.

here is a rough calculation i did on the element.

V = 240 volts
R = 233.3 ohm’s
240/233.3 = 1.028amp
V*amps = watts
240*1.028=246.89 watts

so this element is 250 watts thereabouts

Our Fridge freezer data loggers

1. record the room temperature.
2. record the fridge  temperature.
3. record the freezer  temperature.
4. record the wattage (amperage) so you can see when the motor (compressor) is running or defrost element etc.
5. transmits and record data to graph for months at a time if need.
6. connect to any location with wi-fi so you can veiw data any where with web access in the world.
7. can have alarms built in to send you text warnings that a unit is too warm or too cold.

If you need more info on our system please contact us