Hitachi Summit RAC-18YH6, Service Manual, Page: 59 / 96

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6-6. Electric expansion valve control circuit
Electric expansion valve is driven by B-12V. Opening of the valve is controlled by feeding power to 1
or 2 phases of the 4-phase coil to switch the polarity of the coil.
The relation between the conducting phase switching direction and open/close direction is as shown
below. When the power is turned on, approx. 0.9 V is applied to CN15 pins 1 to 4 ; when no power
is supplied, approx. 12 V is applied. When the power is reset, expansion valve performs initial
operation for 5 to 10 seconds.During initial operation, measure pins 1 to 4 of CN15 using
multimeter: If no change is found around 0.9 V or 12V, expansion valve or microcomputer is
defective.
Fig. 6-15 shows logic waveform during the operation of expansion valve.
1
2
3
4
1
2
3
4