What are the common methods and disadvantages of charging refrigerants

What are the common methods and disadvantages of charging refrigerants
　　 1. Observe the bubbles in the sight glass;
　　2, measure high and low pressure;
　　3. Measure compressor current;
　　4. Weigh the punch.
　　 We need to understand that if the refrigerant charge in the Refrigerant charging pipe is too low, the cooling capacity will decrease, the input power will decrease, the EER will decrease, and the equipment life will be shortened. If the refrigerant is charged too much, the cooling capacity will decrease, the input power will increase, EER will decrease, and the equipment life will be shortened.
　　 1. Observe the bubbles in the sight glass:
　　 This method does show that there is a bubble indicating a lack of refrigerant, but we must understand that the pressure loss of the liquid pipe can also cause bubbles. If the pressure loss of the liquid pipe is large, the liquid refrigerant will flash into a gas, and the flash gas will reduce the flow of the refrigerant when flowing through the expansion valve and will also corrode the expansion valve. If the subcooling of the system is small, the pressure loss can easily generate bubbles seen in the sight glass. Remember, if there is no liquid but steam, it will be transparent when seen in the sight glass.
　　 If the refrigeration engineer with experience or careful observation will find that when the system is charged correctly, bubbles or flashes can also be seen in the sight glass. This is because the resistance in the liquid pipe in front of the sight glass causes a pressure drop, causing the refrigerant to flash. If the expansion valve is unstable or fluctuates with liquid, the expansion valve opens sharply, and the flow rate increases to produce enough pressure drop to cause the outlet of the liquid reservoir to flash. The sudden change in condenser pressure is also the cause of flash.