Basic Knowledge of Cold Storage Maintenance

I. Characteristics and Requirements of Cold Storage Buildings
Cold storage is mainly used for the freezing processing and cold storage of food. It maintains a certain low temperature indoors through artificial refrigeration. The walls, floors, and flat roofs of the cold storage are all lined with thermal insulation materials of a certain thickness to reduce the heat entering from the outside.

II.

Classification of Cold Storage by Temperature:
High-temperature Cold Storage (Freshness Preservation Cold Storage);
Medium-temperature Cold Storage (Refrigeration Cold Storage);
Low-temperature Cold Storage (Quick Freezing Cold Storage);
Freshness Preservation Cold Storage: Preservation storage, or freshness preservation storage, mainly focuses on keeping freshness. That is, within a relatively long period, it can maintain the original quality and freshness of some agricultural products to the greatest extent.
Refrigeration Cold Storage: The storage temperature of the refrigeration cold storage is -18°C. Generally speaking, a refrigeration cold storage means that food is put into the cold storage irregularly.

After a certain period, the temperature of the cold storage reaches -18°C, and the goods are also taken out irregularly and at any time. There is no specific requirement for this "certain period", and this is a typical refrigeration cold storage.
Quick Freezing Cold Storage: It is a cold storage that can freeze food within a very short time. The characteristic of a quick freezing cold storage is that a specified quantity of items is put into the cold storage, and after a specified time, the central temperature of the food reaches the specified temperature, and then all the items are taken out of the warehouse at once. This is a typical quick freezing cold storage.

III. Temperature Control Range of Cold Storage:
Freshness Preservation Cold Storage: +5 ~ -5°C, suitable for preserving vegetables, fruits, and dried foods;
Refrigeration Cold Storage: -10 ~ -20°C, suitable for frozen meat products, poultry, fish, and shrimp;
Quick Freezing Cold Storage: -20°C ~ -45°C, suitable for quickly freezing fresh products, tangyuan (sweet dumplings), dumplings, and other products that need quick freezing in a short time;

IV. Structure Classification of Cold Storage Bodies:
Combined Plate-type Cold Storage;
Civil Construction Cold Storage;
Overburden Cold Storage;

V. Classification of Cooling Methods of Cold Storage:
Direct Evaporation Type;
Indirect Cooling Type;
Currently, the refrigeration system adopted in China is a compression refrigeration system, and the liquid supply methods of the refrigeration system include:
Direct Expansion Liquid Supply Type, Gravity Liquid Supply Type, and Pump Circulation Liquid Supply Type. These three liquid supply methods are determined according to the size of the cold storage and the form of the cooling equipment.

VI.

Main Components of Cold Storage:
The cold storage body is assembled from the bottom plate of the storage body, side plates (thermal insulation wall panels), top plates (ceiling panels), corner plates, and doors. They are spliced and fixed through specially structured male-female hooks to ensure good thermal insulation and airtightness of the cold storage. In addition to being able to open flexibly, the cold storage door should be closed tightly and be reliable in use.
The main function of the unit is to make the indoor temperature of the cold storage reach the required temperature. It is mainly composed of components such as a compressor, internal and external fans, an expansion valve, a filter, high and low-pressure protection devices, and water tower pipes, and it is the core part of the entire cold storage. It is necessary to prevent water ingress and water leakage, which may cause the unit to have an electric leakage and burn out the compressor and other components.
The control electrical box is used to control the normal operation of the entire cold storage. It is mainly composed of components such as control lights, switches, a full-computer controller, a circuit breaker, fuses, a timer, and contactors. The control electrical box should be kept away from fire sources, impacts, and be protected against water leakage, short circuits, moisture, and should not be used to store various sundries.
(The Electric Heating Defrosting Method: It uses the electric heater installed on the fins of the evaporator. The heat generated when the heater is powered on removes the frost attached to the fins. When the temperature sensor senses the set temperature indicating the end of defrosting.)

VII. Reasons for Common Faults
Fault Phenomenon: The fault indicator light is on.
Common Reasons: Check if there is a phase reversal; Check if there is a 380V power input.
Fault Phenomenon: The compressor does not start.
Common Reasons: Check if there is power input; Check if there is a refrigerant leakage; Check if the pressure control protection is activated.
Fault Phenomenon: The suction pressure of the compressor is too high.
Common Reasons: The expansion valve is opened too wide; The suction valve of the compressor and the valve plate are not tightly sealed.
Fault Phenomenon: The suction pressure of the compressor is too low.
Common Reasons: The expansion valve is opened too wide; There is dirt in the filter; There is insufficient refrigerant in the refrigeration system.
Fault Phenomenon: The compressor keeps running.
Common Reasons: The pressure controller or the temperature controller malfunctions or does not work properly; The discharge valve or the suction valve plate of the compressor leaks.
Fault Phenomenon: The cooling of the cold storage is not normal.
Common Reasons: The cold storage door is not closed properly; The evaporator coil is too thickly frosted; The efficiency of the compressor is low; The flow rate of the expansion valve is too large or too small; There is air in the system, and the subcooling degree of the condenser liquid is small, resulting in a decrease in the refrigeration capacity; The filter is too dirty with oil, affecting the flow rate; There is insufficient refrigerant in the refrigeration system; There is too much oil accumulation in the evaporator; The temperature-sensitive agent in the thermostatic expansion valve leaks; The thermostatic expansion valve is blocked by ice; The thermostatic expansion valve is blocked by dirt.
Fault Phenomenon: The air blown by the internal fan is not cold, or the indoor temperature is too high or not cold enough.
Common Reasons: Check if the compressor is running normally; Check if there is a refrigerant leakage; Check if the expansion valve is blocked; Check if the external fan is dirty or if the heat dissipation is good; Check if the fan motor blades are faulty; Check if the temperature sensor is in good condition and if its installation position is correct.
Fault Phenomenon: The defrosting function does not work.
Common Reasons: Check if the defrosting sensor is installed correctly; Check if the set defrosting termination temperature is lower than the storage temperature; Check if the temperature controller is in good condition; Check if the heating wire is in good condition and if the pipeline is blocked.
Fault Phenomenon: The compressor does not stop when the set temperature is reached.
Common Reasons: The sensor is not installed correctly and cannot measure the correct value; The compressor contactor malfunctions.
Fault Phenomenon: The compressor operates too frequently.
Common Reasons: The temperature differential value is too small or there is a problem with the setting of the pressure protector; Readjust and increase the temperature differential value and adjust the setting of the pressure protection.