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10. Temperature detection circuit
OH thermistor
CN5
DEF thermistor
CN6
Outdoor temperature thermistor
CN7
• Compressor head surface temperature is detected by OH thermistor circuit, defrost operation temperature is detected
by DEF thermistor circuit, and outdoor temperature is detected by outdoor temperature thermistor circuit.
• Thermistor is a negative resistance element with the following characteristic: Resistance falls when temperature rises,
and increases when temperature falls.
• When compressor is over-heated, resistance of OH thermistor decreases and voltage at pin
rises.
• Voltage at pin
of microcomputer is compared with set value stored inside: If voltage exceeds set value, microcomputer
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judges over-heating and stops operation.
• If outdoor heat exchanger is frosted, heat exchanger temperature will rapidly drop. In response, resistance of DEF
thermistor increases and voltage at pin
microcomputer enters defrost control mode.
• During defrost operation, microcomputer transfers indoor unit defrost condition command from IF transmission output
at SDO pin of interface (pins
• Outdoor temperature is always read in (voltage at pin
then transferred to indoor unit side. According to this value, compressor rotation speed control and operation selection
(outdoor fan ON/OFF, etc.) in dehumidifying mode are performed.
Represented values of the relationship between outdoor temperature and voltage are shown below.
Outdoor temperature
Voltage at pin
(Reference)
When thermistor is open or heat is shut off, pins
circuited, pins
to
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However, OH thermistor detects only short-circuit as error: It will enter a blink mode after 12 minutes or more has
elapsed from the start of compressor operation.
＋5V
＋5V
＋5V
of microcomputer falls. When the voltage falls under the set value,
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and
of microcomputer).
70
72
(℃ )
of CN7 (V)
1
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of microcomputer are set to about 5V, and LD301 blinks 7 times.
Normal: 2.7V or less
OH: 2.7V or more
Return: 2.3V or less
R304
R301
0V
Normal: 2.4V or more
OH: 2.4V or less
R305
Return: 2.9V or more
R302
0V
R306
Refer to Table 10-1
R303
0V
Fig. 10-1
of microcomputer) by outdoor temperature thermistor, and
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Table 10-1
− 10
0
10
1.19
1.69
2.23
to
of microcomputer are set to about 0 V; when thermistor is short-
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– 116 –
62
OH
C301
Microcomputer
AX-6M00
0V
DEF
63
C302
0V
Outdoor
64
temperature
C303
0V
of microcomputer
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20
30
40
2.75
3.22
3.62
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