– 65 –
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
e
5V is
divided by the over heat thermistor and R512 and the voltage at pin
x
of microcomputer.
●
Microcomputer the voltage at pin
x
and the set value stored inside, and when it exceeds the set value,
the 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
c
of microcomputer
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.
●
The microcomputer always reads the outdoor temperature via a thermistor (microcomputer pin
v
voltage),
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
x
-
v
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 10-1
Outdoor temperature (
°
C)
Microcomputer pin
v
voltage (V)
-10
1.19
0
1.69
10
2.23
20
2.75
30
3.22
40
3.62
62
42
0V
+5V
O.H. thermistor
O.H.
Normal 2.7V or less
Over heat 2.7V or more
Reset 2.3V or less
CN4
R512
0V
63
41
0V
+5V
DEF. thermistor
DEF.
Normal 2.4V or more
Over heat 2.4V or less
Reset 2.9V or more
CN5
R513
0V
64
40
0V
+5V
Outdoor temperature
thermistor
Outdoor
temperature
Refer to the table 10-1
CN7
R514
0V
Micro
computer
(AX-8J01)
HIC
Fig. 10-1