1. Clogging of liquid valve capillaries
2. Insufficient amount of refrigerant (including trouble resulting from an insufficient initial charge and from gas leakage)
3. Blocking of low-pressure parts caused by intrusion of foreign objects (moisture, scale, etc.)
4. Crossing (tubing or PCB connectors) with the other compressor thermistor
5. Expansion valve operation failure
6. Accumulation of refrigerant at stopped outdoor units
7. Compressor discharge sensor failure
8. PCB failure (A/D conversion failure)
9. Electrical noise

1. Clogging of capillaries

Trouble: Compressor discharge temperature does not decrease even when the liquid valve is ON.
Check: When the liquid valve is operating and the liquid valve is ON, check that the secondary side of the liquid capillaries is cold.

2. Insufficient refrigerant

Trouble: Liquid effectiveness is poor.
Check: Check whether or not the superheating temperature is declining if the evaporator mechanical valve is opened to 300 pulses or more (after checking for foreign object intrusion).

3. Foreign object intrusion

Trouble: Liquid valve effectiveness is poor.
Check: Check that there is no difference in the condensation or frost conditions between the strainer primary-side and secondary-side tubing.

4. Crossed thermistor

Trouble: The discharge temperature of the other compressor is high although only this compressor is operating. When the liquid valve turns ON, the discharge temperature of the other compressor decreases.

5. Accumulation of refrigerant in stopped outdoor units

Trouble:
• System is OK when all outdoor units are operating, however symptoms of insufficient
  gas occur when a certain outdoor unit is stopped.
• Condensation or frost is visible up to the top of the accumulator of the stopped
  outdoor unit. • After an outdoor unit stops, there is the sound of refrigerant flowing into
  an outdoor unit that was stopped for a long time.
• When an outdoor unit starts after being stopped for a long time, the start is
  accompanied by much vibration.

Check:
• Representative parts include the liquid capillaries (secondary side of capillaries will be
  cool during cooling operation), mechanical valve, mechanical valve bypass check
  valve (sound of refrigerant flow can be heard, and stops when the liquid valve is
  closed), hot gas defrost valve (if valve secondary side remains hot even after much
  time has passed, be careful not to mistake transmitted heat for a valve failure).
• Ice is growing on the lower parts of some outdoor unit heat exchangers but not on
  others. Because this trouble may occur even in outdoor units with a high operating
  rate under conditions of insufficient gas, caution is needed.

6. Sensor failure

Check:
• This alarm is likely to occur when wiring is partially cut. (It is difficult to identify, even
   when continuity is checked.) The detected discharge temperature is high.
• Although such conditions rarely occur, a P02 alarm is likely if the detected discharge
  temperature is low.
• Replace the sensor with another discharge sensor and compare the temperature
  conditions.

7. If the cause is still unknown after checking the above, then it is possible that electrical noise is the cause of the trouble.

1. Replace the sensor.
2. Replace the outdoor unit PCB.
3. Correct the problem locations.