Panasonic U-8MF2E8 Service Manual page 26

4. Output of PCB
4-9. SC Circuit Electronic Control Valve [MOV4]
4-9-1. SC Control (Cooling Mode only)
During cooling operation, the liquid refrigerant which condenses at the outdoor unit heat exchanger flows into
the receiver tank, and SC (sub-cool = supercooling) approaches 0°C. When SC is small and the length of the
tubing connecting the indoor and outdoor units is long, the refrigerant flow in the indoor unit will be reduced sig-
nificantly. To prevent this trouble from occurring, MOV4 operates so as to increase supercooling in the double
tube coil near the outlet of the outdoor unit.
1
In addition, MOV4 controls refrigerant flow volume so that it will not flow back to the compressor in the liquid
state. SH in suction that is difference between the SCG temperature and low pressure sensor temperature is
adjusted to 3-5°C.
Liquid
(SC=0deg)
4-9-2. Discharge temperature control of compressor
When the discharge temperature increases to 95°C or more, MOV 4 opens to 100 pulses to cool down the
compressor. MOV 4 operates according to the state of the discharge temperature between 20 - 480 pulses. This
operation takes priority over SC control.
Liquid
This operation is continued until discharge temperature decreases to 80°C or less.
4-10. Crankcase Heater Control [CH1, CH2]
When the compressor stops, the crankcase heater of its own compressor is turned ON.
SCG
MOV4
(SH control)
SCG
MOV4
(Discharge temperature control of compressoer.)
Gas returns to
accumulator
Refrigerant on the inner side evaporates,
cooling the liquid refrigerant on the outer side.
Liquid
(Large SC)
Liquid returns to
accumulator
Does not fully evaporate,
resulting in liquid back-up.
Liquid
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3WAY SYSTEM
Control Functions