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[5] Oil-Return Control
· Oil-return LEV (SLEV) is determined by the operating capacity of the compressor and outside temperature.
· During compressor stoppage and for 10 minutes after startup, the opening of SLEV is 75.
· When the compressor is stopped, the opening of SLEV is 0.
[6] Outdoor Unit Fan
(1) Control Method
· Depending on the capacity required, outdoor unit fan is controlled by phase control, and corrections are
made using compression temperature (Tc) to keep evaporation temperature (Te) constant.
(2) Control
· Outdoor unit fan stops when compressor is stopped. (Except in the presence of input from snow sensor)
· Operates at full-speed for 5 seconds of startup.
[7] Subcool Coil Control (Linear Expansion Valve (LEV1))
· Controlled every 20 seconds to keep the amount of superheat constant, using bypass outlet/inlet tempera-
tures of the subcool coil (TH2, TH8).
· The degree of opening is controlled, depending on the inlet/outlet temperatures of the subcool coil (TH5,
TH7), high pressure (HPS), discharge temperature (TH1).
When the compressor is stopped, the valve is in the closed position (0).
· During TH8 error, the valve will be fixed at a certain degree of opening.
[8] Circulating composition sensor (CS circuit)
· As shown in the drawing below; the CS circuit has the structure to bypass part of the gas discharged from
the compressor through the capillary tube to the suction side of the compressor, exchange heat before and
after the capillary tube,and produce two phase (gaseous and liquid) refrigerant at the capillary tube outlet.
The dryness fraction of refrigerant at the capillary tube outlet is estimated from the temperature of low pres-
sure two phase (gaseous and liquid) refrigerant at the capillary outlet (TH2) and the pressure (LPS) to calcu-
late the composition of refrigerant circulating the refrigeration cycle (
α
OC). In this series the high-pressure
liquid refrigerant temperature is calculated based on the high pressure and ambient air temperature values. It
is found by utilizing the characteristic that the temperature of two phase (gaseous and liquid) R407C under a
specified pressure changes according to the composition and dryness fraction (gas-liquid ratio in weight).
· The condensing temperature (Tc) and the evaporating temperature (Te) are calculated from
α
OC, high pres-
sure (HPS), and low pressure (LPS).
· The compressor frequency, the outdoor fan, and others are controlled according to the codensing tempera-
ture (Tc) and the evaporating temperature (Te).
· CS circuit configuration (Outline drawing)
Four-way valve
Compressor
Accumulator
CS circuit
TH2
LPS
Heat e
(HPs)
xchanger
Outdoor heat e
xchanger
Indoor heat
e
xchanger
Flo
w control
valv
e
