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9. Electric expansion valve control circuit
CN15
Electric
expansion
valve
• 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 po wer 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 microcomputer has failure.
• The logic waveform during the operating of the expansion valve is shown in Fig. 9-2.
Table 9-1
CN15
pin#
④
③
②
①
④
③
②
①
POWER P.W.B
Lead
wire
1
2
ON
ON
White
OFF
ON
Yellow
Orange
OFF
OFF
OFF
OFF
Blue
Operation mode
1→2→3→4→5→6→7→8 VALVE CLOSE
8→7→6→5→4→3→2→1 VALVE OPEN
50ms.
Fig. 9-1
Driving state
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
– 142 –
MAIN P.W.B
Microcpmputer
Valve4
Valve3
Valve2
Valve1
7
8
OFF
ON
OFF
OFF
OFF
OFF
ON
ON
12V
0.9V
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