Hitachi RAM-130QH5, Service Manual, Page: 63 / 84

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The electric expansion valve is driven by DC 12V. Power is supplied to 1 or 2 phases of 4-phase winding
to switch magnetic pole of winding in order to control opening degree.
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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 CN15~CN17 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~CN17 using mutimeter. If there is any
pin with voltage that has not changed from around 0.9V or 12V, expansion valve or microcomputer is
defective.
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Fig. 11-2 shows logic waveform when expansion valve is operating.
11. Electric expansion valve
Pin
Drive status
Lear
wire
1
ON
OFF
OFF
OFF
Pin No.
12V
0.9V
200ms
75ms 50ms
42, 38
41, 37
40, 36
39, 35
ON
ON
OFF
OFF
ON
OFF
OFF
ON
OFF
ON
OFF
OFF
OFF
ON
ON
OFF
OFF
OFF
ON
OFF
OFF
OFF
ON
ON
OFF
OFF
OFF
ON
2 3 4 5 6 7 8
White
Blue
Operation mode
VALVE CLOSE
VALVE OPEN 1
8 2
7 3
6 4
5 5
4 6
3 7
2 8
1
Yellow
Orange
phase No.
4
3
2
1
Table 11-2
Fig. 11-2
Table 11-1
With expansion 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.