Hitachi RAS-25CNH1 - Temperature Detection Circuits; Temperature Detection Circuit Diagram

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10. Temperature Detection Circuit
● The Over heat thermistor circuit detects the temperature at the surface of the compressor head, the
Defrost. thermistor circuit detects the defrosting operation temperature.
● A thermistor is a negative resistor element which has the characteristics that the higher (lower) the
temperature, the lower (higher) the resistance.
● When the compressor is heated, the resistance of the Over heat thermistor becomes low and e5V is
divided by the over heat thermistor and R301 and the voltage at pin & of HIC.
● HIC the voltage at pin & and the set value stored inside, and when it exceeds the set value, the micro
computer judges that the compressor is overheated and stops operation.
● When frost forms on the outdoor heat exchanger, the temperature at the exchanger drops abruptly.
Therefore the resistance of the Defrost. thermistor becomes high and the voltage at pin * of HIC drops.
If this voltage becomes lower than the set value stored inside, the micro computer starts defrosting control.
● During defrosting operation the micro computer transfers the defrosting condition command to the indoor
microcomputer via the SDO pin IF transfer output of the interface.
CN4
17
5
Over heat
thermistor
+5V
R301
0V
0V
Over heat
Normal: 2.7V or less
Over heat: 2.7V or more
Reset: 2.3V or less
18
5
Defrost
thermistor
+5V
0V
Defrost
R302
0V
17
5
Over heat
thermistor
+5V
R301
0V
0V
Over heat
Normal: 2.7V or less
Over heat: 2.7V or more
Reset: 2.3V or less
Normal: 2.4V or more
Defrost: 2.4V or less
Reset: 2.9V or more
CN5
Micro computer
(AX-8E21)
HIC
Fig. 10-1