Electric Expansion Valve - Hitachi RAM-130QH5 Service Manual

11. Electric expansion valve

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.
Relationship between power switching direction of phase and open/close direction is shown below.
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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.
Fig. 11-2 shows logic waveform when expansion valve is operating.
●
Pin No.
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.
Lear
Pin
phase No. wire
1 2
4 ON ON
White
3
Yellow OFF ON
2 OFF OFF
Orange
1
OFF OFF
Blue
Operation mode
1 2 3 4 5 6
8 7 6 5 4 3
42, 38
41, 37
40, 36
39, 35
50ms
Table 11-1
Table 11-2
Drive status
3 4 5
OFF OFF OFF OFF
ON ON OFF OFF
OFF ON ON
OFF OFF OFF
7 8 VALVE CLOSE
2 1 VALVE OPEN
75ms
200ms
Fig. 11-2
– 75 –
6 7 8
OFF ON
OFF OFF
ON OFF OFF
ON ON ON
12V
0.9V