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9. Electric expansion valve control circuit
CN15
6
5
4
3
Electric
2
expansion
valve
1
• To drive the expansion valve, use the B-12 V output. Use a 4-phase coil and feed power to the
phases 1 and 2, then switch over the filed poles to control the opening of the valve.
• The reference between conducting phase switch over direction and the open/close direction are
shown in Table 9-1. When the power is turned on, approx. 0.9 V is applied to the CN15 and the pins
( 1 to 4 ) and when no power is supplied, 12 V is applied. When the power is reset, the expansion
valve starts initial operation for 5 to 10 seconds.
• During the initial operation, measure each pin of the CN15 ( 1 to 4 ) with a multimeter. If no change
is found around 0.9 V or 12V in this step, the expansion valve or the micro computer has failure.
• The logic waveform during the operating of the expansion valve is shown in Fig. 9-2.
CN15
Pin No.
④
③
②
①
④
Pin No.
③
②
①
POWER P.W.B.
B-12V
R401
1 8
15
2
10
7
+
4 5
12 13
C401
B-0V
Lead
wire
1
2
White
ON
ON
Yellow
OFF
ON
Orange
OFF
OFF
Blue
OFF
OFF
Operation mode
1→2→3→4→5→6→7→8 VALVE CLOSE
8→7→6→5→4→3→2→1 VALVE OPEN
50ms.
B-12V B-12V
R403 R404
PQ401
14
PQ402
3
PQ403
11
PQ404
6
IC6
Fig. 9-1
Table 9-1
Drive status
3
4
5
6
OFF
OFF
OFF
OFF
ON
ON
OFF
OFF
OFF
ON
ON
ON
OFF
OFF
OFF
ON
75ms.
200ms.
Fig. 9-2
- 65 -
MAIN P.W.B.
5V
Microcomputer
R293
1
11
39
R294
10
2
40
R295
4
8
41
R296
3
9
42
CN4B
CN4A
7
8
OFF
ON
OFF
OFF
OFF
OFF
ON
ON
12V
0.9V
Valve4
Valve3
Valve2
Valve1
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