Panasonic U-72MF2U9 Service Manual page 26

4. Output of PCB
4-10. SC Circuit Expansion Valve [MOV4]
4-10-1. 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-cooling) approaches 32°F (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 significantly.
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.
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
5.4deg F ~ 9deg F (3deg C ~ 5deg C).
1
Liquid
(SC=0deg)
2
3
4-10-2. Discharge temperature control of compressor
When the discharge temperature increases to 194°F (90°C) or more, MOV4 opens to 100 pulses to cool down the
compressor. MOV4 operates according to the state of the discharge temperature between 20 - 480 pulses. This
operation takes priority over SC control.
4
5
6
This operation is continued until discharge temperature decreases to 176°F (80°C) or less.
7
4-10-3. Discharge temperature and high pressure control in outdoor unit cycle defrost control
When outdoor unit cycle defrost control operates, MOV4 opens to 200 pulses or over.
4-11. Crankcase Heater Control [CH1, CH2]
8
When the compressor stops, the crankcase heater of its own compressor is turned ON in the following conditions.
● When the discharge temperature ≤ the outdoor air temperature + 27deg F (+15deg C)
● When the outdoor air temperature ≤ 68°F (20°C)
● When the compressor stops and 30 minutes later.
9
(SH control)
Liquid
(Discharge temperature control of compressor.)
SCG
Gas returns to
accumulator
Refrigerant on the inner side evaporates,
cooling the liquid refrigerant on the outer side.
Liquid
(Large SC)
MOV4
SCG
Liquid returns to
accumulator
Does not fully evaporate,
resulting in liquid backup.
MOV4
1 - 18
3WAY VRF SYSTEM
Control Functions
Liquid