Hitachi RAS-70YH5 Service Manual page 73

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
G
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.
G
When power is supplied, voltages at pins 4 to 1 of CN15 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 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.
G
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.
0305E Pg 57-82
Lear
Pin
phase No. wire
1
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
Pin No.
42, 38
41, 37
40, 36
39, 35
50ms
81
Table 11-1
Table 11-2
Drive status
2 3 4 5 6
OFF OFF OFF OFF
ON ON OFF OFF
OFF ON ON ON
OFF OFF OFF ON
7 8 VALVE CLOSE
2 1 VALVE OPEN
75ms
200ms
Fig. 11-2
– 81 –
4/1/06, 10:59 AM
7 8
OFF ON
OFF OFF
OFF OFF
ON ON
12V
0.9V