Hitachi RAC-25FX8, Service Manual

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– 94 –
R301
5V
R305
C302
64
1
2
3
4
5
0
0 10 20 30 40
3. Room Temperature Thermistor Circuit
A room temperature thermistor circuit is shown in Fig. 3-1.
According to room temperature, the voltage of point becomes as it is shown in Fig.3-2.
Microcomputer
Room Temperature
Thermistor
Vo
ltage of point
(V)
( ℃ ) Room temperature
Room
temperature input
Fig. 3-1
Fig. 3-2
◯ A
0V
0V
5V
20
2
0
1
0
3
4
5
40
10 30 -10
R302
C303
R306
63
1
2
3
0V 0V
R308
0V
C305
C301 R304
5V
4.0
25 ℃
3.5
3.0
2.5
2.0
1.5
1.0
60
80
20 40
＋
−
％
0V
62
4. Heat Exchanger Thermistor Circuit
Heat exchanger temperature is noticed inside the room
(1) Preheating
(2) Low-temperature defrosts at cooling
･
dehumidification operation time.
(3) Not working of reversing valve or detection of opening of heat exchange thermistor is controlled.
According to heat exchange temperature, the voltage of point becomes as it is shown in Fig. 4-2.
Heat exchanger
thermistor Microcomputer
Heat exchanger
input
5. Humidity Sensor Circuit
Humidity sensor
Microcomputer
From the output ( ② pin) of humidity sensor, the 5V pulse of different width is
output according to detected humidity. Smooth output pulse is carried out by
C301 and it changes into the characteristic of voltage-humidity as shown in
Fig.5-2. The micro computer detects and controls humidity by reading this
voltage directly.
Fig. 4-1
Fig. 5-1
Fig. 5-2
Fig. 4-2
V
oltage of point (V)
V
oltage (V)
℃
Room temperature ( )
Humidity ( )
Humidity
◯
A