Hitachi RAS-25CNH2 Service Manual page 35

5. Room Temperature Thermistor Circuit
Fig. 5-1 shows the room temperature
G
thermistor circuit.
5V
Room
temperature
thermistor
R309
R310
A
0V
6. Heat exchanger temperature thermistor circuit
The circuit detects the indoor heat
G
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 A depends on the heat
exchanger temperature as shown in
Fig. 6-2.
Micro
computer
Room
3
temp. input
C302
0V
Fig. 5-1
5V
Heat exchanger
temperature thermistor
R307
R308
A
0V
Fig. 6-1
The voltage at A depends on the room
G
temperature as shown in Fig. 5-2.
5
4
3
2
1
0
0
Micro computer
Heat
4
exchanger
C301
temperature
input
0V
5
4
3
2
1
0
-10 0
Heat exchanger temperature (˚C)
– 38 –
10 20 30
Room temperature (˚C)
Fig. 5-2
10 20 30
Fig. 6-2
40
40