Chapter 6. Failure Diagnosis; Outline Of Control; Check Mode Of Defrost Heater (Forced Defrosting) - Sharp SJ-A20S-SL Service Manual

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SJ431NSL
CHAPTER 6.
FAILURE DIAGNOSIS

[1] OUTLINE OF CONTROL

1. ON/OFF Control of Compressor
When the plug of refrigerator is connected, the compressor will start automatically and run for approximately 5 minutes. After then, ON/OFF of the
compressor will be controlled depend on the temperature detected by the R-thermistor. During 6 minutes after the compressor stops, it will not start
regardless of the detected temperature by R-thermistor..
2. Defrosting
Microcomputer calculates the appropriate timing of defrosting and defrosting is made automatically. Therefore no manual operation by user is
required. The cycle of defrosting varies depend on the usage condition of the refrigerator. (Maximum time 50 hours, minimum time 4 hours)
3. Thermistor
Thermistors are installed in 2 places; in the refrigerator compartment and close to the
Evaporator. (R-thermistor and Def-thermistor)
It is not installed in the freezer compartment.
R-thermistor reads the temperature in the refrigerator compartment and controls ON/OFF
of compressor.
Def-thermistor detects the temperature around the evaporator and shows the progress of
defrosting.

[2] CHECK MODE OF DEFROST HEATER (Forced Defrosting)

The operation of the defrost heater can be checked by starting it.
In case the failure of defrosting is suspected, this is an effective inspection method.
1. Starting Method
At the power OFF condition.
1) Keep the door of the refrigerator compartment open.
2) Set the Temp. Control Knob in the refrigerator compartment to the following position.
220-240V models: Center
110-127V models: Max
3) Keep the door open and supply power source.
2. Normal Operation
1) Approximately 3 seconds after power supply, the relay on the PWB will be turned ON and the defrost heater will be electrified for 5 seconds.
2) After 5 seconds, if the temperature of Def-thermistor reaches high enough (over 10°C) and judged as defrosting completion, the compressor runs
for 5 minutes and then returns to the normal control.
On the other hand, if the temperature of Def-thermistor is still low (under 10°C), the defrost heater will be electrified until the temperature of Def-
thermistor reaches the specified temperature or higher.
After completion of electrification, the compressor runs for 5 minutes and then returns to the normal control.
* In the case that any abnormality in Door Switch, Volume, R-thermistor or Def-thermistor, or the Temp. Control Knob is not in the position corre-
sponding to the value of the rating voltage settled to the PWB itself, this mode will not be entered nor the defrost heater is electrified.
Service Manual
PWB
(Center)
6 – 1
Def-thermistor
Evaporator
Defrost heater
R-thermistor
Compressor