Hitachi RAC-18SX8 Service Manual page 157

5. Electrical expansion valve circuit
6
5
4
3
2
1
CN19
(unmounted)
6
5
4
3
2
1
Electrical
expansion
valve 1
Red
CN15
XA-6P
6
5
4
3
2
1
CN21
(unmounted)
・The electrical expansion valve is driven with a 12 V DC power source, which is designed specifically for
the expansion valve. Four phases of windings are energized for 1 or 2 phases, while the magnetic
poles of the windings are switched over to control the valve aperture. (It is insulated from
microcomputer potential.)
・The switchover direction of energization phases and the opening/closing direction are as shown in Table
5-1. When energized, pins ① to ④ of CN15 are at about 1.2 V, and when not energized, they are at about
12 V. When the power supply is reset, the expansion valve is initially operated for 30 to 40 seconds.
During initial operation, the pins ① to ④ of CN15 are measured with a tester. If there is any pin which
shows no change at 1.2 V or 12 V, then either the expansion valve or microcomputer should be
abnormal.
・Fig. 5-2 shows the logical waveform generated when the expansion valve is operating.
C411
1 20
GND VDD
2 19
ENABLE RES
3 18
LATCH CLK
4 17
S-OUT S-IN
5 16
B-0V P-GND P-GND
6 15
COM2 COM1
7 14
05 04
8 13
06 03
9 12
07 02
10 11
08 01
IC11
C421
1 20
2 19
3 18
4 17
5 16
B-0V
6 15
7 14
8 13
9 12
10 11
IC12(unmounted)
B-0V B-0V
B-12V
B-0V
R416
R417
B-0V
B-0V
４
３
PQ401
R411
B-0V
R412
4
B-0V
3
PQ402
B-0V
4
3
PQ403
R413
B-0V
Fig. 5-1
– 190 –
＋
C401
5V
１
２
HIC
5V
IC2
R356
16
34
1
R357
2
15
35
R358
36 14
5V
1
2
Microcomputer
Clock signal
1 32
Latch signal
2 33
Serial signal
3 34