Hitachi RAS-50YH4 Service Manual page 55

5. Room Temperature Thermistor Circuit
Fig. 5-1 shows the room temperature
●
thermistor circuit.
5V
Room
temperature
thermistor
R305
R301
A
0V
6. Heat exchanger temperature thermistor circuit
The circuit detects the indoor heat
●
exchanger temperature and controls
the following.
(1) Preheating.
(2) Low-temperature defrosting
during cooling and dehumidifying
operation.
(3) Detection of the reversing valve
non-operation or heat exchanger
temperature thermistor open.
The voltage at
heat exchanger temperature as shown
in Fig. 6-2.
Microcomputer
Room
62
temp. input
C302
0V
Fig. 5-1
5V
Heat exchanger
temperature thermistor
R306
R302
A
0V
Fig. 6-1
depends on the
A
The voltage at
●
temperature as shown in Fig. 5-2.
5
4
3
2
1
0
0
Microcomputer
Heat
61
exchanger
C303 temperature
input
0V
5
4
3
2
1
0
0
-10
Heat exchanger temperature (˚C)
– 65 –
depends on the room
A
10 20 30
Room temperature (˚C)
Fig. 5-2
10 20 30
Fig. 6-2
40
40