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1. The internal and external units of the multi-online machine are running normally, no refrigeration, no heating, cold and heat: the air conditioning system cannot effectively absorb and release heat through sufficient refrigerant circulation, resulting in the indoor ambient temperature cannot be stabilized at the set value, and the phenomenon of no refrigeration, no heating, and cold and hot occurs.
2. Compressor exhaust temperature protection, frequency reduction operation: When the refrigerant is insufficient, the compressor needs to work at a lower refrigerant flow, which may lead to an increase in the internal exhaust temperature of the compressor. To prevent overheating damage, a protection mechanism built into the system is activated to limit the operating frequency of the compressor (frequency reduction) to reduce the operating intensity and temperature. This frequency-reduced operation is a self-protective response of the system to a lack of refrigerant.
3. High and low pressure protection of the compressor, reduced frequency operation: insufficient refrigerant will lead to the internal pressure imbalance of the system, and the pressure on the high-pressure side may be too low (due to the lack of refrigerant in the condenser, the heat exchange efficiency will be reduced) or the pressure on the low-pressure side will be too high (due to the lack of refrigerant in the evaporator, the heat absorption capacity will be reduced). In both cases, the compressor may trigger high and low pressure protection and be forced to operate at reduced frequency to avoid further pressure anomalies that can damage the compressor.
4. Two condensing fans of the external unit, one turning, the other not rotating: Under normal circumstances, the condensing fans of the multi-online external unit should work synchronously to ensure good heat dissipation effect. Insufficient refrigerant can cause the condensing pressure to drop, and the system judges that the load demand is reduced, so that only one fan is turned on to maintain the basic cooling needs, while the other remains turned off.
5. Extended running time or frequent start-up: In order to reach the set indoor temperature, the air conditioner needs to run for a longer time, and may start and stop frequently, because the system efficiency decreases due to insufficient refrigerant, and it cannot effectively absorb and transfer heat.
6. The opening of the electronic expansion valve is 100% or significantly increased: the electronic expansion valve automatically adjusts the opening according to the system pressure and temperature feedback to control the flow of refrigerant. When the refrigerant is insufficient, the system may adjust the electronic expansion valve opening to the maximum (i.e., 100%) in order to maximize the flow of refrigerant through the evaporator, and even increase significantly beyond the normal range under certain conditions in an attempt to compensate for the decrease in refrigeration efficiency caused by the lack of refrigerant.
7. Some internal units do not work: In the multi-online system, if the total amount of refrigerant is insufficient to supply all indoor units for normal operation, it may cause some indoor units to fail to start or maintain effective refrigeration due to insufficient refrigerant distribution. At this time, although other indoor units may still be running, the cooling efficiency of the entire system is greatly reduced, and some areas cannot be effectively cooled.
8. The temperature difference between the inlet and outlet air of the multi-online indoor unit is reduced, and the effect is poor: under normal working conditions, the air inlet of the indoor unit sucks in room temperature air, and after the evaporator is cooled, the air outlet sends cold air, and there should be a certain temperature difference between the two, and the temperature difference is generally 8 °C ~ 15 °C. When the refrigerant is insufficient, the cooling efficiency of the evaporator is reduced, so that the temperature difference between the air inlet and outlet of the indoor unit is significantly reduced.
9. The suction and exhaust temperature of the compressor rises (bias flow), the superheat becomes larger, and the temperature of the liquid pipe of the outdoor engine decreases: the refrigerant in the evaporator is insufficient due to the insufficient refrigerant, and the evaporation pressure and temperature drop, which makes the suction temperature of the compressor low; at the same time, due to the lack of refrigerant in the condenser, the condensing pressure and temperature drop, and the compressor discharge temperature will also be low. Combined, these two phenomena manifest as an increase in the suction and exhaust temperature of the compressor (in fact, it refers to the "bias" phenomenon of low suction temperature and high discharge temperature relative to normal operating conditions). In addition, due to the reduced heat transfer efficiency of the condenser, the refrigerant does not fully release heat during the condensation process, so the temperature of the outdoor engine liquid pipe (i.e., the condensed liquid refrigerant pipe) will drop.
10. Compressor frequency reduction (if the refrigerant is insufficient, the heating operation frequency will be high, but the pressure difference has a tendency to become larger): In the case of insufficient refrigerant, even if the compressor is operated at a reduced frequency to reduce the load, due to the internal pressure imbalance of the system, especially the increase of the pressure difference between the high and low pressure sides, the actual operating frequency of the compressor in the heating mode may be high.
11. Low pressure alarm or fault code display: Multi-online air conditioning system is usually equipped with a pressure sensor and a corresponding control system, when the low pressure on the low pressure side of the system is too low due to insufficient refrigerant, a low pressure alarm may be triggered or a fault code related to insufficient refrigerant may be displayed on the control panel.
12. Frosting or freezing of the evaporator: In the case of insufficient refrigerant, the evaporator may have abnormal low temperature due to the decrease in heat absorption capacity, resulting in rapid frosting or freezing on the surface of the evaporator. This not only affects the cooling effect, but can also cause the air conditioner to automatically enter protection mode and stop operating.