Hitachi RAM-68NP3B, Service Manual, Page: 52 / 79

When controlling an expansion valve, the temperature of the compressor head is detected and then the opening is
adjusted to stabilize the valve to the target temperature.
This control cycle is performed once every 20 seconds, and a few pulses are output.
Fig. 5-2
12V
0.9V
160ms
96ms 32ms
①
②
③
④
Connector
Pin No.
Table 5-1
●
There are three electric expansion valves for indoor units 1-3.
●
The electric expansion valves are powered by B-12V for expansion valves. 1- or 2-phase current is applied to
4-phase wound wires, switching the poles of the wound wires to control valve openings.
●
The relationship between the switching direction of the current phase and the open/close direction of the valves is
shown in the following table. When current is applied, approximately 0.9V passes through pins
①
-
④
of CN15,
CN19, and CN26 ; when no current is applied, it is approximately 12V. When the power is reset, the expansion
valve is initialized for approximately 35 seconds. During initialization, use a tester to measure pins
①
-
④
on CN15, CN19, and CN26. If there is a pin that does not change at approximately 0.9V or 12V, there is an
abnormality in that expansion valve or the main microcomputer.
●
The logic waveform for when an expansion valve operates is shown in Fig. 5-2.
Fig. 5-1
CLK
CLK
C421
7
IC32
8
G
Q
A
SER
Q
G
6
5
SCK
4
3
2
12
11
15
14
13
VDD Q
B
1 16
9
Q
C
Q
D
Q
E
Q
F
Q
H
GND Q
H'
XA-6P
4
2
3
5
6
(BLU)
+
C423
B-12V
CN26
1
SCLR
RCK
10
B-0V
B-0V
1 16
15
5 12
13
3
4
10
8
7
6 11
14
2
B-5V
IC34
9
B-0V
B-0V
C424
C425 C426 C427
58
59
60
8
24
23
22
Main
Microcomputer
Main
Microcomputer
H I C
H I C
B-12V
6
1
2
7
4 5
8 9
3
6
16
1 8 9 16
14 58 Exp valve B4
Exp valve B3
Exp valve B2
Exp valve B1
59
60
61
58
59
60
61
15
10
2
7
15
10
11
3
6
14
11
1213
4 5 1213
5
4 61
62
63
64
65
66
67
68
3
2
1
6
5
4
3
2
1
B-12V
B-12V
IC25
IC24
B-0V
B-0V
B-0V
C401
C516
C515
CN19
XA-6P
（WHT）
Electric
expansion
valve 1
CN15
XA-6P
（ RED ）
5. Electric Expansion Valve Circuit
8
→
7
→
6
→
5
→
4
→
3
→
2
→
1 VALVE OPEN
1
→
2
→
3
→
4
→
5
→
6
→
7
→
8 VALVE CLOSE
OFF OFF
OFF OFF OFF OFF OFF ON ON ON
OFF OFF OFF ON ON ON
OFF OFF
ON ON ON
OFF OFF OFF OFF OFF
ON ON OFF OFF OFF ON
8 7 6 5 4 3 2 1
Power conditions
Blue
Orange
Yellow
White
Lead wire
①
②
③
④
CN15, CN19, CN26
Pin No.
Operation mode
Electric
expansion
valve 2
Exp valve B4
Exp valve B3
Exp valve B2
Exp valve B1
Electric
expansion
valve 3
Serial 1
Latch
Serial 1
Latch
Reset
Circuit