Hitachi RAC-25FX8, Service Manual

Page: 124 / 191

– 142 –
Fig. 9-1
Table 9-1
Fig.9-2
POWER P.W.B
MAIN P.W.B
Electric
CN15
expansion
valve
Microcpmputer
Valve4
Valve3
Valve2
Valve1
CN15
pin#
Lead
wire
Driving state
White
Yellow
Orange
Blue
Operation mode
• 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.
9. Electric expansion valve control circuit
④
③
②
①
1→2→3→4→5→6→7→8 VALVE CLOSE
8→7→6→5→4→3→2→1 VALVE OPEN
④
③
②
①
12V
0.9V
50ms. 75ms.
200ms.
1
ON
OFF
OFF
OFF
2
ON
ON
OFF
OFF
3
OFF
ON
OFF
OFF
4
OFF
ON
ON
OFF
5
OFF
OFF
ON
OFF
6
OFF
OFF
ON
ON
7
OFF
OFF
OFF
ON
8
ON
OFF
OFF
ON