Indoor Electronic Expansion Valve Control - Hitachi RCI-1.0FSR Service Manual

4 Control system

Indoor electronic expansion valve control

4.12 Indoor electronic expansion valve control
1 After supplying power, the electronic expansion valve closes fully before starting to open.
2 When the compressor stops, the electronic expansion valve closes fully to set its opening.
3 When it starts (the compressor is activated), the electronic expansion valve opens to a specific degree during cooling
operation, 1 minute.
4 During heating operation, the electronic expansion valve opens to a specific degree.
5 During defrost, the electronic expansion valve opens to a specific degree, as indicated in the graph.
6 Normal opening of the electronic expansion valve.
Cooling operation
1 The required setting of the superheat (SH) temperature is determined by the system based on the detected Indoor
gas pipe temperature (Tg) and Indoor liquid pipe temperature (TL).
2 Simulated PI control for the electronic expansion valve.
The opening of this valve is controlled so that the SH temperature of the heat exchanger can reach the set
temperature.
Heating operation
1 The required setting of the superheat (SH) temperature is determined by the system based on the detected Indoor air
inlet temperature (Ti), Indoor liquid pipe temperature (TL) and Outdoor temperature (Ta).
2 Simulated PI control for the electronic expansion valve.
The opening of the electronic expansion valve is controlled so that the temperature of the indoor liquid pipe can reach
the set temperature.
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Checking method of electronic expansion valve
1 Check that the voltage of the valve ranges between
12Vdc±1.2V.
2 Use a multimeter to check the coil resistance (per
phase). This ranges between 100 Ω±10% at an ambient
temperature of 20°.
3 Check the number of pulses per second. This ranges
between 100Ω ± 250 pulses per second (the width
between pulses is greater than 3 mm ) on activating
phase 2.
4 Check that the valve flow is reversible.
5 When the valve is fully open and in heating process,
check that the temperature of the liquid in the piping
increases. If not, this indicates a fault.
6 When the valve is slightly open or fully open, check
that the temperature of the freeze protection thermistor
is higher than the suction temperature. If not, this
indicates a fault.
91 SMGB0137 rev.0 - 05/2021
Time chart
Defrost
Heating
Opening of
electronic
expansion
valve (pulse)
thermistor temperature
30 sec.
Depending on
of compressor
Electronic
expansion valve coil
Electronic expansion
valve body
Blue
(4)
Yellow
(1)
Red
(6)
(5)
(3)
Orange
White
(2)
Free
Electronic expansion
valve connector
4