Hitachi RAC-25FPA, Service Manual

Page: 58 / 117

When power is supplied, the microcomputer reads the data in IC401 (E
2
PROM) and sets the preheating
activation value and the rating and maximum speed of the compressor, etc. to their initial values.
Data of self-diagnosis mode is stored in IC401; data will not be erased even when power is turned off.
Fig. 6-1
Microcomputer
External ROM
SCL
SDA
0V
0V 0V
5V
5V 5V
C401
IC401 (E
2
PROM)
R404 R403
82
81
1
2
3
4
8
7
6
5
}
The temporary switch is used to operate the air conditioner temporarily when the wireless remote control
is lost or faulty.
The air conditioner operates in the previous mode at the previously set temperature. However, when the
power switch is set to OFF, it starts automatic operation.
Fig. 7-1
TEMPORARY SW
MICROCOMPUTER
R629
SW211
Temporary
switch
0V
0V
C642
R734
54
5V
6. Initial Setting Circuit (IC401)
7. Temporary Switch Circuit
R301
5V
R305
C302
90
1
2
3
4
5
0
0 10 20 30 40
8. Room Temperature Thermistor Circuit
A room temperature thermistor circuit is shown in Fig. 8-1.
According to room temperature, the voltage of point becomes as it is shown in Fig.8-2.
Microcomputer
Room Temperature
Thermistor
V
oltage of point
(V)
(
℃
) Room temperature
Room
temperature input
Fig. 8-1
Fig. 8-2
◯ A
0V
0V
5V
2
0
1
0 10 20 30 40
3
4
5
-10
R302
C303
R306
91
9. Heat Exchanger Thermistor Circuit
Heat exchanger temperature is noticed inside the room
(1) Preheating
(2) Low-temperature defrosts at cooling
and 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. 9-2.
Heat exchanger
thermistor
Microcomputer
Heat exchanger
input
Fig. 9-1
Fig. 9-2
V
oltage of point (V)
℃ Heat temperature ( )
◯
A
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