Initial Setting Circuit; Temporary Switch Circuit; Room Temperature Thermistor Circuit; Heat Exchanger Thermistor Circuit - Hitachi RAC-18WEC Service Manual

6. Initial Setting Circuit (IC531)
When power is supplied, the microcomputer reads the data in IC531 (E 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 IC531; data will not be erased even when power is turned off.

7. Temporary Switch Circuit

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.

8. Room Temperature Thermistor Circuit

A room temperature thermistor circuit is shown in Fig. 8-1.
According to room temperature, the voltage of point
5V
Room Temperature
Thermistor
R406
R403
A
Fig. 8-1

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
5V
Heat exchanger
thermistor
R407
R402
A
0V
Fig. 9-1
5V
Temporary
switch
SW211
0V
Fig. 7-1
Microcomputer
Room
90
temperature input
C404
Microcomputer
Heat exchanger
91
input
C403
0V
2
Fig. 6-1
MICROCOMPUTER
R405
TEMPORARY SW
100
0V
becomes as it is shown in Fig.8-2.
becomes as it is shown in Fig. 9-2.
5
4
3
2
1
0
0 10 20 30 40
Room temperature
Fig. 8-2
5
4
3
2
1
0
0 10 20 30 40
-10
Heat temperature
Fig. 9-2