Mitsubishi City Multi PURY-P400 Service Handbook page 46

(9) Outdoor unit heat exchanger capacity control
1) Control method
• In order to stabilize the evaporation temperature during cooling and the high-pressure pressure during heating that
are required in response to performance needs, the capacity of the outdoor heat exchanger is controlled by regulat-
ing the fan volume of the outdoor unit by phase control and controlling the number of fans and by using the solenoid
valves to vary the number of out door heat exchangers being used.
2) Control
• When both of the compressors are stopped, the fans for the outdoor units are also stopped.
• The fans operate at full speed for 5 seconds after starting.
• The fans for the outdoor unit are stopped during defrosting.
3) Capacity control pattern
Operation mode Operation pattern
Full cooling
Cooling mainly
Full heating
Heating mainly
Defrosting
* In stop, all are OFF.
(10) 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 compres-
sor 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 high pressure liquid refrigerant at the capillary tube inlet
(TH9) and the temperature of low pressure two phase (gaseous and liquid) refrigerant at the capillary outlet (TH2) and
the pressure (LPS) to calculate the composition of refrigerant circulating the refrigeration cycle (αOC). 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 αOC, high pressure
(HPS), and low pressure (LPS).
• The compressor frequency, the outdoor fan, and others are controlled according to the codensing temperature (Tc)
and the evaporating temperature (Te).
• CS circuit configuration (Outline drawing)
Four-way valve
Accumulator
SV3 SV4
ON ON
ON ON
OFF ON
OFF ON
OFF OFF
OFF OFF
ON ON
ON ON
OFF ON
OFF ON
OFF OFF
OFF OFF
OFF OFF
ON ON
ON ON
ON ON
ON ON
OFF OFF
ON ON
Heat exchanger
TH9
TH2
LPS
CS circuit
–45–
Solenoid valve
SV5 SV6
ON OFF
ON OFF
ON OFF
OFF OFF
ON OFF
OFF OFF
ON OFF
ON OFF
ON OFF
OFF OFF
ON OFF
OFF OFF
OFF ON
ON OFF
ON OFF
ON OFF
ON ON
OFF ON
ON OFF
SV7 SV8
ON ON
OFF OFF
OFF OFF
OFF OFF
OFF OFF
OFF OFF
ON ON
OFF OFF
OFF OFF
OFF OFF
OFF OFF
OFF OFF
OFF OFF
ON ON
ON ON
OFF OFF
OFF OFF
OFF OFF
ON ON