Hitachi RAM-50CNHZ2, Service Manual, Page: 84 / 107

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12. Electric expansion valve
●
The electric expansion valve is driven by DC 12V. Power is supplied to 1 or 2 phase winding to switch
magnetic pole of winding in order to control opening degree.
●
Relationship between power switching direction of phase and open/close direction is shown below.
When power is supplied, voltages at pins
4
to
1
of CN 15 and CN 16 are about 0.9V; they are about 12V
when no power is supplied. When power is reset, initialization is performed for 10 or 20 seconds.
During initialization, measure all voltages at pins
4
to
1
of CN15 and CN16 using tester. If there is any pin
with voltage that has not changed from around 0.9V or 12V, expansion valve or microcomputer is defective.
●
Fig 12-2 shows logic waveform when expansion valve is operating.
2
8 1 9 16
1
2
3
4
5
6
3 39
15 14 40
7 6 41
10 11
42
4 5 12 13
Microcomputer
Valve
Valve
Valve
Valve
B
A
B
A
IC6, 7
5V
R208
12V
12V
C225
R209
O
CN15, 16
Electric expansion valve 1
V
Fig. 12-1
Pin Lear
phase No. wire
4
4 5 6 7 8
3
3
2
2
1
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
1
1
White
Yellow
Orange
Blue
ON ON
ON ON ON
ON ON ON
ON ON ON
ON
OFF
OFF
OFF
OFF OFF OFF OFF
OFF
OFF OFF OFF OFF OFF
OFF
OFF OFF
OFF OFF
OFF
OFF
Drive status
Table 12-1
Operation mode
VALVE CLOSE
VALVE OPEN
200ms
75ms
Fig. 12-2
50ms
39, 35
40, 36
41, 37
42, 38
Pin No.
12V
0.9V
With explosion valve control, opening degree is adjusted to stabilize target temperature, by detecting temperature
of compressor head.
The period of control is about once per 20 seconds, and output a few pulses.