Signs of a Normal Cold Storage and Troubleshooting

2025-05-06

Reasons for Poor Refrigeration Effect of the Cold Storage

Refrigerant Leakage
[Fault Analysis] After the refrigerant leaks in the system, the refrigeration capacity is insufficient, the suction and discharge pressures are low, and a much louder intermittent "squeaking" airflow sound can be heard at the expansion valve compared to normal. The evaporator does not frost or only has a small amount of floating frost. If the expansion valve hole is adjusted larger, there is still no significant change in the suction pressure. After the machine stops, the balance pressure in the system is generally lower than the saturated pressure corresponding to the same ambient temperature.
[Solution] After the refrigerant leaks, do not rush to charge the refrigerant into the system. Instead, immediately find the leakage point, and charge the refrigerant after repair.
Excessive Refrigerant Charged After Maintenance
[Fault Analysis] When the amount of refrigerant charged into the refrigeration system after maintenance exceeds the system's capacity, the refrigerant will occupy a certain volume of the condenser, reducing the heat dissipation area, lowering its refrigeration efficiency. The suction and discharge pressures are generally higher than the normal pressure values, the evaporator does not frost solidly, and the temperature in the cold storage drops slowly.
[Solution] According to the operation procedure, the machine should be stopped for a few minutes, and then the excess refrigerant should be released at the high-pressure stop valve. At this time, the residual air in the system can also be released together.
Air in the Refrigeration System
[Fault Analysis] The presence of air in the refrigeration system will reduce the refrigeration efficiency. The prominent phenomenon is that the suction and discharge pressures increase (but the discharge pressure has not exceeded the rated value), and the temperature from the compressor outlet to the condenser inlet increases significantly. Due to the air in the system, both the discharge pressure and the discharge temperature rise.
[Solution] After the machine is stopped for a few minutes, air can be released from the high-pressure stop valve several times in a row. Some refrigerant can also be appropriately charged according to the actual situation.
Low Compressor Efficiency
[Fault Analysis] The low efficiency of the refrigeration compressor means that under the condition that the working conditions remain unchanged, the actual exhaust volume decreases, resulting in a corresponding reduction in the refrigeration capacity. This phenomenon mostly occurs in compressors that have been used for a long time. Due to large wear, the clearance between various components is large, and the sealing performance of the air valve decreases, leading to a decrease in the actual exhaust volume.
[Solution]
⑴ Check whether the cylinder head paper gasket is broken through and causes leakage. If so, replace it.
⑵ Check whether the high and low-pressure exhaust valve plates are not closed tightly.
If so, replace them.
⑶ Check the clearance between the piston and the cylinder. If the clearance is too large, replace it.
Excessive Frost on the Evaporator Surface
[Fault Analysis] The evaporator of a cold storage that has been used for a long time should be defrosted regularly. If not defrosted, the frost layer on the evaporator pipeline will accumulate thicker and thicker. When the entire pipeline is covered with a transparent ice layer, it will seriously affect heat transfer, resulting in the temperature in the cold storage not dropping to the required range.
[Solution] Stop the machine for defrosting, open the cold storage door to let the air circulate, or use a fan, etc. to accelerate the circulation and reduce the defrosting time.
Refrigeration Oil in the Evaporator Pipeline
[Fault Analysis] During the refrigeration cycle, some refrigeration oil remains in the evaporator pipeline. After a long time of use, when there is a large amount of residual oil in the evaporator, it will seriously affect its heat transfer effect, resulting in poor refrigeration.
[Solution] Remove the refrigeration oil in the evaporator. Remove the evaporator, blow it out, and then dry it. For those that are not easy to remove, you can use a compressor to blow air from the evaporator inlet and then dry it with a blowtorch.
Unsmooth Refrigeration System
[Fault Analysis] Due to the unclean cleaning of the refrigeration system, after a certain period of use, dirt gradually accumulates in the filter, and some mesh holes are blocked, resulting in a reduction in the refrigerant flow rate and affecting the refrigeration effect. There are also slight blockage phenomena in the filters at the expansion valve and the compressor suction port in the system.
[Solution] Remove the slightly blocked components, clean and dry them, and then reinstall them.
Filter Blockage
[Fault Analysis] The desiccant is used for a long time and becomes pasty to block the filter, or dirt gradually accumulates in the filter to cause blockage.
[Solution] Remove the filter, clean and dry it, replace the new desiccant, and install it back into the system.
Refrigerant Leakage in the Temperature Sensing Bulb of the Expansion Valve
[Fault Analysis] After the temperature sensing agent in the temperature sensing bulb of the expansion valve leaks, the two forces below the diaphragm push the diaphragm upward, closing the valve hole. The refrigerant in the system cannot pass through, resulting in no refrigeration. At this time, the expansion valve does not frost, the low pressure is in a vacuum state, and no airflow sound can be heard in the evaporator.
[Solution] Stop the machine and close the stop valve. Remove the expansion valve to check whether the filter is blocked. If not, you can blow into the expansion valve inlet with your mouth to see if it is unobstructed. You can also check it visually or by disassembling it. Replace it if it is damaged.
The Compressor Stops Suddenly During Operation
Poor Heat Dissipation Effect of the Cold Storage with Air-cooled Condenser
[Fault Analysis]
① The fan is not turned on.
② The fan motor is damaged.
③ The fan is running in the reverse direction.
④ The ambient temperature is high (reaching above 40℃).
⑤ The condenser fins are blocked by oil stains and dust, and the air does not circulate.
Poor Heat Dissipation Effect of the Cold Storage with Water-cooled Condenser
① The cooling water valve is not opened or is opened too small, and the inlet water pressure is too low.
② The water volume regulating valve fails.
③ The scale on the wall of the condenser is relatively thick.
[Solution]
For air-cooled type: Use a wire brush to remove the surface dust.
For water-cooled type: Check the cooling water volume. Remove the scale.
Excessive Refrigerant Charged into the System
[Fault Analysis] Excessive refrigerant leads to a significant increase in the discharge pressure, exceeding the normal value.
[Solution] Stop the machine and discharge the excess refrigerant out of the system through the high-pressure exhaust hole.
Residual Air in the System
[Fault Analysis] When there is air circulation in the system, the discharge pressure will be too high, the discharge temperature will be high, the exhaust pipe will be hot to the touch, the refrigeration effect will be poor. Soon after the compressor runs, the discharge pressure exceeds the normal value, forcing the pressure relay to act.
[Solution] Stop the machine and release the air at the exhaust valve hole.
Shutdown Caused by Too Low Suction Pressure
[Fault Analysis] When the suction pressure in the system is lower than the set value of the pressure relay, its contacts will act and cut off the power supply.
[Solution] Check the cause and eliminate it: 1. Refrigerant leakage. 2. Blockage in the system.
Temperature Controller Malfunction
[Fault Analysis] The temperature controller is malfunctioning in adjustment or the temperature sensing bulb is installed improperly.
[Solution] Remove the temperature controller, repair its contacts, make adjustments, and adjust the position of the temperature sensing bulb.
Motor Overload
[Fault Analysis] 1. When in use, too much food is put into the cold storage; 2. The power supply is abnormal.
[Solution] Reduce the heat load and pay attention to the changes in the power supply voltage.
Sudden Shutdown Caused by Other Reasons
[Fault Analysis] During the use and maintenance process, it is often necessary to open and close the stop valves of the exhaust, suction, and liquid receiver, etc. Sometimes, due to negligence, the stop valve is not opened, resulting in a sudden increase in the exhaust pressure.
[Solution] Stop the machine immediately to prevent danger.
Signs of Normal Operation of the Cold Storage
There should be no abnormal noise in the cylinder, only the normal and regular rise and fall sound of the suction valve plate in the cold storage.
The suction temperature of the compressor should be 5-15℃ higher than the evaporation temperature (R22).
The cooling water of the condenser should be sufficient, the water pressure should be above 0.12mpa, and the water temperature should not be too high.
For new series products, the reading of the oil pump pressure gauge should be 0.15-0.3mpa higher than the suction pressure.
There should be no excessive heating or frosting on the cylinder wall. The surface temperature difference should not be greater than 15-20 degrees. For cold storage or low-temperature systems, the suction pipe can generally frost up to the suction port; for high-temperature working conditions, the suction pipe should not frost, and it is normal to have condensation.
The oil temperature in the crankcase of the fluorine refrigeration machine should not exceed 70 degrees, and the lowest should not be lower than 10 degrees. There can be foam in the lubricating oil of the fluorine refrigeration machine.
The exhaust temperature should not be too high. For R22 products, it should not exceed 135 degrees. If it is too high and close to the flash point (160 degrees) of domestic refrigeration oil, it will be detrimental to the equipment.
The condensation pressure should not be too high. For R22 water-cooled systems, it should not exceed 1.8mpa. The condensation pressure is affected by the construction force of the cold storage, and it varies according to the water source, condensation method, and refrigerant.
The oil level in the crankcase should not be lower than 1/2 of the horizontal center line of the oil sight glass.
It is normal for the automatic oil return pipe of the fluorine oil separator to be hot and cold alternately. There should be no obvious temperature difference before and after the liquid pipe filter of the cold storage, and it should not frost. Otherwise, it is blocked. The cylinder head should be half cold and half hot, and there should be no oil leakage at each joint.
When touching the horizontal liquid receiver and oil separator by hand, the upper part should be hot and the lower part should be cold. The boundary between hot and cold is the liquid level or oil level. The safety valve or bypass valve on the low-pressure side should feel cool. Otherwise, there is crossflow of high and low pressure.
During operation, the evaporation pressure and the suction pressure should be approximately the same, and the discharge pressure, condensation pressure, and the pressure of the liquid receiver should be similar.
There should be a temperature difference between the inlet and outlet of the cooling water. If there is no or a very small temperature difference, it indicates that the heat exchanger is dirty and needs to be cleaned.
The refrigeration machine should be sealed, and there should be no leakage of refrigerant or lubricating oil. There should be no dripping oil at the shaft seal of the fluorine refrigeration machine.
The temperature of the shaft seal and bearing of the refrigeration machine should not exceed 70 degrees.
The expansion valve body should frost or condense evenly, but there should be no thick frost at the inlet. When the fluid passes through the expansion valve, only a dull and slight sound can be heard.
The pointer of each pressure gauge in the system should be relatively stable, and the temperature indication should be correct.
Signs of Normal Operation of the Compressor Lubrication System
The indication of the oil pressure gauge in the cold storage should be stable. For piston refrigerators, the indicated pressure should be 0.05-0.3MPA higher than the suction pressure, and for screw refrigerators, it should be 0.2-0.3MPa higher than the condensation pressure.
The oil temperature in the crankcase should be maintained between 10-65℃, and the most suitable working temperature is 35-55℃.
The oil level in the crankcase should be sufficient and remain stable for a long time.
The filter element of the oil filter should not be blocked. For the fine oil filter with a differential pressure signal, there should be an indication of blockage.
Maintenance of the Cold Storage Lubrication System Should Pay Attention to
Regularly check the oil quality according to the oil change indicators specified for the refrigeration lubricating oil, and replace or replenish the filtered new oil.
Regularly replace or clean the filter element, pipeline, and crankcase.
Pay attention to observing whether the oil level, oil temperature, and oil pressure are normal during daily spot checks.
During medium and major overhauls, pay attention to checking and adjusting the end clearance of the oil pump, and replace the pump if necessary.