Electric Expansion Valve Control Circuit - Hitachi RAS-18FH6 Service Manual

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.
IC6
4
3
2
1
4
3
2
1
– 57 –
HIC