Why vacuum the cold storage? How to charge refrigerant?

July 28, 2021

      Why does the refrigeration system emphasize the vacuum? Let’s first look at the composition of the air. As shown in the diagram below, nitrogen is 78% , oxygen is 21% and other gases are 1% . What is the effect of the composition of these gases on the refrigeration system once they enter the system?


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1、 Impact of air on the system

      1. Impact of nitrogen in the air on the system:

First of all, we should know that nitrogen is a non condensable gas. The so-called non condensable gas means that the gas circulates in the system with the refrigerant, does not condense with the refrigerant, and does not produce refrigeration effect.

The existence of non condensable gas does great harm to the refrigeration system, which is mainly reflected in the increase of system condensation pressure, condensation temperature, compressor exhaust temperature and power consumption. Nitrogen enters the evaporator and cannot evaporate with the refrigerant; It will also occupy the heat exchange area of the evaporator, so that the refrigerant can not be fully evaporated and the refrigeration efficiency will be reduced; At the same time, too high exhaust temperature may lead to carbonization of lubricating oil, affect the lubrication effect, and burn down the refrigeration compressor motor in serious cases.

Effect of oxygen in the air on the system:

Oxygen and nitrogen are also non condensable gases. We have analyzed the hazards of non condensable gases above, and we will not repeat here. However, it should be noted that compared with nitrogen, if oxygen enters the refrigeration system, it also has these hazards:

The oxygen in the air will react with the refrigeration oil in the refrigeration system to produce organic matter, and finally form impurities, which enter the refrigeration system, resulting in dirty blockage and other adverse consequences.

Oxygen and refrigerant, water vapor, etc. are easy to form acid chemical reaction, which will oxidize the refrigeration oil. These acids will damage all components of the refrigeration system and damage the insulation layer of the motor; At the same time, these acid products will stay in the refrigeration system without any problems at first. As time goes by, they will eventually lead to the damage of the compressor. The following figure illustrates these problems well.

Effects of other gases on refrigeration system:

Water vapor affects the normal operation of the refrigeration system. The solubility in Freon liquid is the smallest, and the solubility decreases gradually with the decrease of temperature. The most intuitive impact of water vapor on the refrigeration system is as follows, which we will explain in graphic way:

There is water in the refrigeration system. The first impact is the throttling structure. When the water vapor enters the throttling mechanism, the temperature decreases rapidly, and the water reaches the freezing point, resulting in icing, blocking the small through hole of the throttling structure, resulting in the failure of ice blockage.

The water vapor from the corroded pipeline enters the refrigeration system, and the water content of the system increases, resulting in corrosion and blockage of pipelines and equipment.

Produce sludge deposits. In the process of compressor compression, water vapor encounters high temperature and refrigeration oil, refrigerant, organic matter, etc., resulting in some series of chemical reactions, resulting in motor winding damage, metal corrosion and formation of sludge deposits.

To sum up, in order to ensure the effect of refrigeration equipment and prolong the service life of refrigeration equipment, it is necessary to ensure that there is no empty gas in the refrigeration system. Therefore, the air should be excluded from the system in the correct way. In the practical application of refrigeration system, sediment and corrosion will cause blockage and failure of expansion valve, filter dryer and filter screen. The only reliable way to make the refrigeration system discharge the water vapor in the air is to take the correct operating steps and use the deep vacuum pump.

For the newly installed unit, the vacuum pump must be used to vacuum the whole refrigeration system. It is not allowed to use the compressor of the unit to vacuum the system, otherwise it may cause irreparable damage to the compressor.

2、 Refrigerant filling in cold storage system

For the working procedure of filling refrigerant into the refrigeration system of the unit, the refrigerant filling operation shall be carried out after the vacuum pumping of the refrigeration system, so as to prevent the infiltration of air due to the vacuum in the system.

Before filling the refrigeration system of the unit with refrigerant, the circuit of the solenoid valve in the system shall be connected to make it open. When adding refrigerant for the first time, fill liquid refrigerant from the high-pressure valve stop valve of the unit or the filling port on the reservoir. If possible, a dry filter can be installed on the filling pipe between the unit and Freon cylinder to prevent moisture and impurities in the refrigerant from entering the system.

The first filling amount of refrigerant can be 80% of the rated value of refrigeration system demand, and the first filling amount should not be too much.

For large refrigeration systems, after filling, the unit will stand still for about 30 minutes. After the internal pressure of the refrigeration system of the standby group is stable, the compressor can be started (for water-cooled units, the cooling water system should be started first) to observe the operation state of the refrigerant. Generally, the flow state of the refrigerant can be observed from the system mirror to judge whether the refrigerant filling amount is appropriate, If the refrigerant is insufficient, add an appropriate amount of gaseous refrigerant from the low-pressure detection port until the bubbles in the sight glass disappear, the evaporator is full of uniform frost, and the return pipe of the compressor is full of thin frost. It can be determined that the refrigeration dose of the refrigeration system is appropriate.

In most cases, the low-pressure side can be filled with gaseous or liquid refrigerant. When the refrigerant filling amount is large, the high-pressure side can also be filled with liquid refrigerant. Need attention! If liquid refrigerant is charged from the low-pressure side, be sure to add it slowly to avoid liquid hammer! If you are afraid of liquid hammer, you can also fill in gas.

Method of adding refrigerant from low pressure side:

During the operation of filling gaseous refrigerant from the low-pressure side, first rotate the low-pressure three-way stop valve counterclockwise to the end point, then connect the fluorine adding pipe of the fluorine bottle to the bypass screw seat of the low-pressure three-way stop valve, then open the bottle valve of R22 fluorine bottle, slightly loosen the connector of the bypass screw seat of the three-way stop valve, drive out the air in the fluorine adding pipe with R22 gas, and "hiss When the "hissing" air flow sounds, lock it immediately and the refrigerant charging begins.

When the injection volume reaches the specified quality, close the fluorine bottle stop valve, turn the low-pressure three-way stop valve counterclockwise to the end point, close the bottle valve of R22 fluorine bottle, remove the fluorine adding pipe, and the fluorine adding work is completed.