Hitachi RAC25NH4, Руководство по обслуживанию

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9. 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 voltage at
pin
62
of microcomputer is increased.
●
Microcomputer compares the voltage present at pin
62
with the internal set value, if it is exceeded the
set value microcomputer 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
63
of microcomputer
drops.
If this voltage becomes lower than the set value stored inside, the microcomputer starts defrosting control.
●
During defrosting operation the microcomputer transfers the defrosting condition command to the indoor
microcomputer via the circuit interface.
●
The microcomputer always reads the outdoor temperature via a thermistor (microcomputer pin
64
), and
transfers it to the indoor unit, thus controlling the compressor rotation speed according to the value set
at the EEPROM in the indoor unit, and switching the operation status (outdoor fan on/off, etc.) in the dry
mode.
The following shows the typical values of outdoor temperature in relation to the voltage:
<Reference>
When the thermistor is open, in open status, or is disconnected, microcomputer pins
62
–
64
are approx. 0V;
when the thermistor is shorted, they are approx. 5 V, and LD301 blinks seven times.
However, an error is detected only when the OH thermistor is shorted; in such a case, the blinking mode is
entered 12 minutes after the compressor starts operation.
Table 9-1
Outdoor temperature (
°
C)
Microcomputer pin
5
voltage (V)
-10
1.19
0
1.69
10
2.23
20
3.22
40
3.62
62 7
0V
+5V
O.H. thermistor
O.H.
Normal 2.7V or less
Over heat 2.7V or more
Reset 2.3V or less
CN8
63 6
0V
+5V
DEF. thermistor
DEF.
Normal 2.4V or more
Over heat 2.4V or less
Reset 2.9V or more
CN9
64 5
0V
+5V
Outdoor temperature
thermistor
Outdoor
temperature
Refer to the table 10-1
CN10
Microcomputer
HIC
Fig. 9-1
2.75
30