Multi-split air conditioner: Nitrogen charging for welding, pressure maintaining, vacuuming and refrigerant charging

Nitrogen-filled Welding
Why is nitrogen-filled welding necessary? What are the benefits of nitrogen-filled welding?
Since nitrogen has very stable chemical properties, the purpose of nitrogen-filled protection is to prevent oxide scale from forming on the inner walls of copper pipes at high temperatures. While the air contains oxygen, an oxidation reaction will occur when welding copper pipes, and oxides will be produced. Let's take a look at the comparison diagram of the cross-sections of copper pipes with and without nitrogen-filled welding. Obviously, the inside of the pipe with nitrogen-filled welding on the right is smooth and free of oxides. It should be noted that impurities such as oxides may cause clogging in the system and seriously damage the compressor.
When performing nitrogen-filled welding on pipelines, the following knowledge is required:
① During welding, the nitrogen pressure should be controlled at around 0.2 - 0.

3 kgf/cm2.
② The gas used must be nitrogen. The use of oxygen is prohibited to avoid the risk of explosion!
③ Ensure that the path of nitrogen flows through the welding point being operated.
④ Ensure sufficient nitrogen inflow time to ensure that the air at the welding position is completely discharged.
⑤ The welding work should preferably be carried out downward or horizontally sideways, and back welding should be avoided as much as possible.

Pressure Maintenance
After welding is completed, a pressure test must be carried out on the copper pipes. Fill the copper pipes with nitrogen at a certain pressure for pressure maintenance. Slowly inject nitrogen from the low-pressure process port. If there is a liquid solenoid valve in the system, first turn on the solenoid valve by electrifying it, and hang a positive pressure gauge at the high-pressure process port to detect the pressure.
For R410A refrigerant, the pipe pressure needs to be maintained at 40 kg, and for R22 refrigerant, the pressure inside the pipe needs to be maintained at 20 kg. The duration of pressure maintenance depends on the refrigeration equipment. Generally, 8 hours is sufficient for household multi-split air conditioners, and the cold storage system usually requires a pressure maintenance time of more than 12 hours. Note that it is still strictly prohibited to use oxygen for pressure maintenance. Oxygen may easily cause an explosion when it comes into contact with the refrigeration oil in the refrigeration system.
It should be noted that changes in the ambient temperature can cause changes in the nitrogen pressure. For every ±1 °C difference in the ambient temperature, there will be a pressure difference of ±0.1 kgf/cm2.
Correction method:
Actual value = Pressure at pressurization ~ (Temperature at pressurization ~ Temperature at observation) × 0.1 kgf/cm2. By comparing the corrected value with the pressurization value, it can be seen whether the pressure has dropped.

Vacuum Pumping
Why is vacuum pumping necessary?
Because air belongs to non-condensable gases. Non-condensable gases refer to gases that circulate in the system along with the refrigerant, do not condense with the refrigerant, and do not produce a refrigeration effect.
The existence of non-condensable gases has great harm to the refrigeration system, mainly manifested as follows: It will cause the system's condensation pressure to rise, the condensation temperature to rise, the compressor's exhaust temperature to rise, and the power consumption to increase. Nitrogen entering the evaporator cannot evaporate with the refrigerant; it will also occupy the heat exchange area of the evaporator, preventing the refrigerant from evaporating fully and reducing the refrigeration efficiency. Meanwhile, due to the excessively high exhaust temperature, the lubricating oil may be carbonized, affecting the lubrication effect, and in severe cases, burning out the motor of the refrigeration compressor. The normal vacuum degree of the system should be able to reach below ~756 mmHg (~0.1 Mpa).

Refrigerant Charging
Refrigerant should be charged through the refrigerant charging process port. If the system does not have a reserved refrigerant charging port, it should be charged through the high-pressure process port. The weighing charging method is the most standard method, which is applicable to any refrigeration system. The method is to weigh the amount of refrigerant charged. As long as the manufacturer indicates the exact charging amount on the nameplate. It should be noted that a large amount of liquid refrigerant should not be charged through the low-pressure process port to avoid liquid slugging of the compressor.
According to the regulations of air conditioner installation or maintenance processes (national standards or relevant industry standards): When the connection pipeline between the indoor and outdoor units of the air conditioner exceeds the standard length by more than 5 meters, the refrigerant should be replenished in a timely manner. According to different pipeline specifications or air conditioner models with different cooling capacities, use an electronic scale to quantitatively add refrigerant.
The amount of refrigerant added is calculated based on the diameter and length of the liquid-side pipes connecting the outdoor unit and the indoor unit, with the refrigerant being R22 or R410A. For the additional sealing of the refrigerant, please add and seal the refrigerant in a liquid state from the liquid pipe.