Refrigerators must know how to operate: nitrogen welding, pressure maintaining, vacuuming, and adding refrigerant

Refrigerators must know how to operate: nitrogen welding, pressure maintaining, vacuuming, and adding refrigerant

1. Nitrogen filled welding

Why do we need nitrogen filled welding? What are the benefits of nitrogen filled welding? Due to the stable chemical properties of nitrogen, the purpose of nitrogen protection is to prevent the formation of oxide scale on the inner wall of copper pipes at high temperatures. And the air contains oxygen, which will undergo oxidation reaction when welding copper pipes, producing oxides.

Notes:

① The nitrogen pressure should be controlled between 0.2-0.3kgf/cm ² Left and right.

② The gas used must be nitrogen, and the use of oxygen is prohibited to avoid the risk of explosion!

③ Ensure that the path of nitrogen flows through the solder joint being operated on.

④ Sufficient nitrogen injection time should be ensured to ensure that the air at the welding position is completely discharged.

⑤ Welding work should be carried out downwards or horizontally to avoid backwelding as much as possible.

2. Maintaining pressure

After welding is completed, a pressure test must be carried out on the copper pipe. A certain pressure of nitrogen gas is filled into the copper pipe to maintain pressure. Nitrogen gas is slowly injected from the low-pressure process port. If there is a liquid circuit in the system, the solenoid valve should be energized and opened first. A positive pressure gauge should be hung at the high-pressure process port to test the pressure.

R410A refrigerant needs to maintain a pipe pressure of 40 kilograms, while R22 refrigerant needs to maintain a pipe pressure of 20 kilograms. The duration of pressure holding depends on the refrigeration equipment. Generally, for home installations, multiple units can be connected for 8 hours, while for cold storage systems, the pressure holding time is generally more than 12 hours. Attention, it is still strictly prohibited to use oxygen for pressure maintenance. Oxygen in contact with the refrigeration oil in the refrigeration system can easily cause explosions!

It should be noted that changes in ambient temperature can cause changes in nitrogen pressure. For every ± 1 ℃ temperature difference in ambient temperature, there will be a pressure difference of ± 0.1 kgf/cm2.

Correction method: Actual value=Pressure during pressurization - (Temperature during pressurization - Temperature during observation) x 0.1 kgf/cm2. By comparing the corrected value with the pressurization value, it can be seen whether the pressure has decreased.

3. Vacuum pumping

Why do we need to vacuum? Because air belongs to non condensable gases, non condensable gases refer to gases circulating in the system with the refrigerant, not condensing with the refrigerant, and not producing refrigeration effects.

The presence of non condensable gases poses great harm to refrigeration systems, mainly manifested 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, preventing the refrigerant from fully evaporating and reducing the refrigeration efficiency; At the same time, high exhaust temperature may cause carbonization of lubricating oil, affecting lubrication efficiency, and in severe cases, burning out the refrigeration compressor motor. The normal system vacuum degree should be below -756mm Hg (-0.1 Mpa).

4. Filling refrigerant

The refrigerant should be added from the refrigerant filling process port. If the system does not reserve a refrigerant filling port, it should be added from the high-pressure process port. The weighing and filling method is the most standard method, which is applicable to any refrigeration system. The method is to weigh the weight of the refrigerant filled. As long as the manufacturer specifies the exact filling amount on the nameplate. It should be noted that a large amount of liquid refrigerant should not be added from the low-pressure process port to avoid causing compressor liquid shock.

According to the regulations of air conditioning installation or maintenance technology (national standards or industry related standards), when the indoor and outdoor unit connection pipeline of air conditioning installation exceeds the standard length by more than 5 meters, refrigerant should be replenished in a timely manner. According to different pipeline specifications or air conditioning models with different cooling capacities, electronic scales are used to quantitatively add refrigerant

The amount of refrigerant added is calculated based on the diameter and length of the liquid side piping connecting the outdoor and indoor units, with refrigerant R22 and R410A. For the additional sealing of refrigerant, please seal the refrigerant in a liquid state from the liquid pipe.