Daikin VRV – Excessive / Insufficient Charging of Refrigerant

For VRV system, troubleshooting can be executed only with the operating conditions of air conditioner relating to pressure control and electronic expansion valve control, and the methods of judgment are shown below.

1. For excessive charging
(The operating capacity of compressor has a tendency to increase in cooling while decrease in heating.)
1. Operate with light load by using capacity control of compressor due to increasing of high pressure (condensing temperature).
(Compressor capacity cannot be controlled to obtain the target pressure.)
As a result, circulation volume of refrigerant decreases, and cooling and heating will malfunction.
2. In heating operation, since a large amount of liquid refrigerant is stagnant between the outlet of condenser and the liquid line, the cooling temperature of refrigerant become large and discharge air temperature lowers even when the target pressure (see below) is maintained in heating operation. Moreover, the detecting temperature of liquid pipe thermistor in indoor unit may be kept at approx. 40°C or higher normally, while in this case, the temperature may lower to approx. 35°C or lower due to a stagnancy of refrigerant. Accordingly, the discharge temperature may become approx. 30°C.
3. In heating operation, the control is executed during closing operation of EV opening degree.
Since the liquid pressure rises with the rising high pressure, even if the EV is throttled to the minimum opening degree (200 pls), refrigerant cannot be super heated at the outlet of heat exchanger and liquid refrigerant which does not evaporate returns to compressor, resulting an operation so called “wet operation”.
• Superheated degree = 0 ? The discharge pipe temperature lowers.
(Condensing temperature + 20°C or less)

2. For insufficient charging
(The operating capacity of compressor has a tendency to decrease in cooling while increase in heating.)
1. The discharge pipe temperature of compressor rises. (Suction SH increases, and discharge pipe temperature also increases.)
2. Refrigerant at the outlet of evaporator is superheated. (Electronic expansion valve will be opened fully.)
In this case, for the suction superheat degree of compressor is increased, alarm display of insufficient gas (U0) is displayed.
3. In cooling operation, when the operation capacity of compressor is small, since the low pressure (evaporating pressure) is low against refrigerant load, the unit cannot be operated with required capacity due to decreasing of refrigerant circulation volume. In heating operation, it is required to check that the difference between high pressure and liquid pressure is 0.3 to 0.4 MPa.

Due to the characteristic of expansion valve, refrigerant cannot flow easily when the pressure difference between inlet and outlet of the valve is 0.2 MPa or more, therefore, liquid refrigerant will be stagnant between indoor heat exchanger and liquid piping.

Large pressure difference ? Shortage of refrigerant
Small pressure difference ? Excessive charge of refrigerant

1 26 Daikin VRV   Excessive / Insufficient Charging of Refrigerant

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