Hi @thuyledinh
The lights in both the freezer and the refrigerator compartments are controlled by their associated door switch.
If they don't turn on at all whenever the appropriate door is opened, then it is either a door switch problem or a wiring problem to the switches or the lamps.
Regarding the no defrost problem, if it goes into the defrost mode and the ice on the evaporator unit isn't being melted it could be a faulty defrost heater or a faulty bi-metal defrost thermostat.
Disconnect the power to the refrigerator and then unplug the defrost heater- part #WP2315530 (supplier example only) which is located under the evaporator unit, from the wiring harness and use an Ohmmeter to test it for continuity. I don't know what its resistance value is but it shouldn't test open circuit.
If the heater is OK, here's a video that shows how to test a bi-metal defrost thermostat -part #WP4387503 (supplier example only). The defrost thermostat is also located near to the evaporator unit inside the freezer compartment.
Here's the tech sheet for the refrigerator that has the wiring diagram. Both the full detailed schematic and the simplified version that may also help, especially if it is a wiring problem with the lights.
If a part is faulty and needs replacing, search online using the part number only to find suppliers that suit you best.
Hi @thuyledinh
That end of the brown and pink wires go nowhere. They are test points as shown in the wiring diagram. The other end of the wires go to the defrost timer - bi-metal defrost thermostat connection and the bi-metal defrost thermostat - heater connection - see image below.
How to read a wiring diagram 101.
In the image are two more images that shows the power path for:
green arrows - normal operation show all the components that receive power during normal operation
red arrows - defrost cycle show all the components that receive power during the defrost cycle
Normal operation
The power to the defrost timer motor, compressor motor, evaporator fan motor and condenser fan motor is controlled the temperature thermostat.
The power to the compressor motor, evaporator fan motor and condenser fan motor is also controlled by the defrost timer thermostat.
The temperature thermostat opens when the correct temperature is reached and this stops the defrost timer motor, compressor motor, evaporator fan motor and condenser fan motor from operating. When the temperature in the compartments warms up, the thermostat closes and reconnects power to the defrost timer motor, compressor motor, evaporator fan motor and condenser fan motor and they start to operate again.
So the temperature is controlled by the thermostat turning the compressor, fans etc on and off to keep the temp within the set limits.
Defrost cycle:
When the defrost timer has operated for a cumulative compressor run time of 8-10 hours the defrost timer contacts switch over and disconnect power to the compressor motor, evaporator fan motor and condenser fan motor and connect power to the defrost heater.
The bi-metal thermostat in the heater path is a safeguard to prevent the evaporator unit from getting too hot and damaging it. It is only thin Aluminium and can be easily damaged by excessive heat from the heater which is directly beneath it. If the temp gets too hot the bi-metal thermostat operates and disconnects the heater. When the temp cools down again it releases and allows the heater circuit to be ready for the next defrost cycle.
The defrost timer motor continues to operate and when the set time for the defrost cycle has elapsed, the contacts switch back and disconnect the power to the defrost heater and connect power again to the compressor motor, evaporator fan motor and condenser fan motor turning them on to get the refrigerator back into normal operation.
At all times the lights and ice maker have power available. It is not controlled by the defrost timer or the thermostat.
(click on image)