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6-4. Temperature Detection Circuit
O.H. thermistor
DEF. thermistor
Outdoor temperature
thermistor
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
negativ resistor element which has the characteristics that the higher (lower) the temperature,
negative
the lower (higher) the resistance.
When the compressor is heated, the resistance of the Over heat thermistor becomes low and voltage to a
pin 59 59 of microcomputer is increased.
of microcomputer is increased.
Microcomputer compares the voltage at pin 59 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.
the resistance of the Defrost. thermistor becomes high and the voltage at pin 63 of microcomputer drops.
If this voltage becomes lo
If this voltage becomes lo
If this v
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 ), an
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
mode.
The follo
The f
The follo
wing shows the typical values of outdoor temperature in relation to the voltage:
Table 6-2
Outdoor temperature
R303 Voltage
<Reference>
When the thermistor is open, in open status, or is disconnected, microcomputer pins 59 , 63 , 64 are
approx. 0V; when the thermistor is shorted, they are approx. 5 V, and LD301 b
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.
Main P.W.B.
+5V
CN8
1
2
+5V
CN9
1
2
+5V
CN10
1
2
wer than the set value stored inside, the microcomputer starts defrosting control.
s
switching
the operation status (outdoor fan on/off, etc.) in the dehumidifying
alues of outdoor temperature in relation to the voltage:
alues of outdoor temperature in relation to the v
(℃ )
(V)
HIC
R304
20
R301
0V
0V
R305
21
R302
0V
0V
R306
22
R303
0V
0V
Fig. 6-12
with the internal set value, if it is exceeded the set value
0
10
− 10
1.19
1.69
2.23
V
V, and LD301 b
- 62
-
OH
59
C304
Microcomputer
AX-8V10
63
DEF
C303
Outdoor
64
temperature
C302
uptly Therefore
uptly.
of microcomputer drops.
20
30
40
2.75
3.22
3.62
links seven times.
Theref
Therefore
), an
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