When a cold storage facility’s cooling performance is poor and the room temperature fails to drop, the most common on-site reaction is "refrigerant shortage". Insufficient refrigerant does lead to reduced cooling capacity, lower suction pressure, and insufficient liquid supply to the evaporator, but judgment should not rely solely on a single phenomenon—especially when combined with superheat and subcooling readings to minimize misjudgments.
Below are the six most easily observable on-site symptoms, along with explanations of other causes that need to be ruled out for each.
1. Slow Cooling and Extended Compressor Operation
When refrigerant is insufficient, the liquid supply to the evaporator decreases, reducing the effective heat transfer area and thus lowering the cooling capacity. Typical on-site manifestations include: significantly slower cooling of the cold storage, failure to reach the set temperature for a long time; continuous compressor operation, reduced downtime, or even non-stop operation for a long time; slower cooling of goods when the incoming stock is large.
If cooling was normal before but the above issues suddenly appear recently, combined with low suction pressure and increased superheat, focus should be placed on checking for refrigerant shortage. However, similar phenomena can also be caused by excessive cold storage load, severe evaporator frosting, poor condenser heat dissipation, or reduced compressor efficiency, which need to be ruled out one by one.
2. Low Suction Pressure and Reduced Evaporation Temperature
Low suction pressure is a common manifestation of refrigerant shortage. Insufficient refrigerant reduces the liquid supply to the evaporator, leading to a drop in evaporation pressure. On-site, the low pressure gauge reading can be used, combined with the pressure-saturation temperature relationship of the refrigerant, to determine if the evaporation temperature is too low.
For example: A cold storage facility using R404A refrigerant was operating stably, but later experienced a drop in suction pressure, uneven evaporator frosting, increased superheat, and reduced cooling capacity. In this case, focus should be on checking for refrigerant shortage.
It should be emphasized that a single low pressure value cannot be used to diagnose refrigerant shortage. Normal suction pressure varies among different cold storage facilities due to differences in evaporation temperature, room temperature, cooling load, and refrigerant type. If low suction pressure is accompanied by significantly high superheat, the possibility of refrigerant shortage is higher; if low suction pressure is not accompanied by high superheat, the evaporation load, expansion valve, and liquid supply pipeline should be checked.
3. Uneven Evaporator Frosting, with Possible No Frosting in the Rear Section
When refrigerant is insufficient, it may evaporate completely in the front section of the coil, leaving insufficient liquid refrigerant in the rear section for heat transfer. On-site manifestations include: relatively obvious frosting in the front section of the evaporator, reduced frosting in the middle and rear sections, or even no frosting in some coils, leading to reduced overall heat transfer efficiency and slow room temperature drop.
In a direct expansion system, this situation requires focusing on whether the evaporator liquid supply is uniform and whether the outlet superheat is too high. However, uneven frosting does not necessarily mean refrigerant shortage—insufficient expansion valve opening, clogged filters or distributors, uneven liquid distribution in coils, or fan failures can all cause similar phenomena. If only local frosting occurs while other parts have almost no frosting, combined with significantly high superheat, further inspection of the liquid supply system is needed.
4. Recommended Diagnosis Sequence
First, check the cooling trend and compressor operation duration, then read the suction pressure and calculate the evaporation temperature, and finally cross-verify with the frosting pattern and superheat. When all three directions point to the same conclusion, add refrigerant to avoid misdiagnosing expansion valve or fan issues as refrigerant shortage and refilling repeatedly.
The stable operation of a cold storage facility relies on the combined support of insulation, unit matching, and daily inspections. Guizhou Hongya Glacier Refrigeration Equipment Co., Ltd. will archive unit selection, pipeline configuration, and commissioning parameters when delivering cold storage projects, to facilitate customers’ subsequent maintenance and troubleshooting.
Guizhou Hongya Glacier Refrigeration Equipment Co., Ltd.
2026-10-27
