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CONTROL
⑤ Subcooling valve control
Subcooling valve is used for the following purposes: Subcooling demand control • Subcooling demand con-
trol of the outdoor heat exchanger (cooling only) • Apparent engine speed control (cooling only) • Upper limit
control of the intake degree of superheat • Intake temperature avoidance lower limit control • Intake degree
of superheat lower limit control (heating only)
1. Subcooling valve open position range
In cooling : 0 ~ 500 steps
In heating : 0 ~ 500 steps
2. Initial open position
In cooling : Standard open position for apparent engine speed
In heating : 0 steps
3. Control during normal operation
<Cooling>
This control works so that the degree of subcool at the outlet of the outdoor unit and the degree of subcool
of the outdoor heat exchanger meet the standard value.
However, this control sets the upper limit of open position so that the intake degree of superheat is not too
small, and also sets the lower limit of open position so that the intake temperature is not too high.
<Heating>
This control works so that the degree of subcool of the liquid pipe at the inlet of the outdoor unit meets the
standard value.
However, this control sets the upper and lower limit of open position so that the intake degree of superheat
is not too small, and also sets the lower limit of open position so that the intake temperature is not too high.
6) Defrosting (In Heating Only)
In heating, frost formation on the outdoor heat exchanger blocks heat absorption from the outside air, and causes
deterioration of heating capacity. Defrost control is necessary to prevent such a problem.
Defrost control
1. Judgment for starting defrosting
1) Judgment of frost formation
The control system judges frost formation based on the relationship between defrosting detection tempera-
ture and outside air temperature, and starts defrost control.
2) Defrosting prohibiting conditions
Defrost control does not start if the following conditions are satisfied, even if the system detects frost forma-
tion.
Under starting control
When the specified length of time has not passed since the last defrost control, or start of remote control
operation or temperature control.
2. How defrost control starts
Defrost control starts as follows.
(1) Oil return control is terminated when oil return control is working.
(2) The control system sends defrosting signal to all indoor units.
(3) The control system controls apparent engine speed and hot gas bypass valve so that refrigerant high-low
pressure difference meets the specified value.
(4) Reversing valve is turned OFF when the refrigerant high-low pressure difference meets the specified
value.
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