Common refrigerant charging methods for central air conditioners

In practical applications, the following methods are often used to detect whether the refrigerant in the refrigeration system is sufficient. Let’s analyze the drawbacks of these charging methods:

1, touch the suction pipe and exhaust pipe with your hands to sense the cold and heat of the copper pipe;

2, observe the bubbles in the sight glass;

3, measure high and low pressure;

4, measure the compressor current;

5, calculate the degree of superheat;

6. ​​Observe the condensation on the suction pipe;

7. Weigh the punch.

1. Touch the suction pipe and exhaust pipe to sense the heat and cold of the copper pipe

Everyone has different feelings about cold and heat. If your hands have calluses, then the temperature you perceive is higher than the actual temperature. Usually, the human body feels hot to temperatures above 37°C and cold to temperatures below 37°C. The temperature limit of skin perception is 49℃, so the liquid pipe temperature perceived by your hand is not necessarily a good condensation temperature.

2. Observe the bubbles in the sight glass

This does show that there are bubbles that indicate a lack of refrigerant, but 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.

If you see that the bubbles in the sight glass are caused by pressure loss rather than insufficient refrigerant, then you continue to add refrigerant to eliminate the bubbles, you will find that the high pressure rises and causes the machine to trip. This method cannot correctly judge the refrigerant charge of the system.

3, measure high and low pressure

This method is used more, but it should be noted that the condensing air volume and the evaporating air volume are not satisfied, which will affect the refrigerant pressure tested. If the condensing air volume is insufficient, the high pressure will be very high, and if the evaporating air volume of the expansion valve system is insufficient, the low pressure will be very low. Before you test the system pressure, you must confirm that the condensing air volume and evaporating air volume are sufficient. The fin coil and filter should be clean, and the fan speed should be correct; check that the fan blades are not deformed or damaged, and are correctly installed on the shaft.

4, Measure compressor current

This method is used more, but it should be noted that the current tested under different conditions is also different. For example, the current is affected by the main power voltage value, and the deviation of the voltage value causes the deviation of the current.

5. Calculate superheat

The superheat is calculated by measuring the suction temperature and pressure value of the suction pipe on the evaporator. The pressure value is converted into the temperature value minus the difference of the suction temperature value, which is the superheat.

But it should be noted that if the system is flushed to ensure the correct degree of superheat in a cold day, the system will experience excessive refrigerant in a hot day. For the expansion valve system, it is easy to overcharge. Because the expansion valve will automatically open and close, the excessive or insufficient refrigerant flow through the coil will maintain the same superheat. If you realize this, it will cause condensation More refrigerant accumulates in the device, causing high-pressure rise, high current, and compressor loss.

6. Observe the condensation on the suction pipe

When the capillary system is flushing refrigerant, the condensation of the suction pipe will be observed. This flushing method depends on the refrigerant liquid flow rate of the capillary tube and the pressure difference between both ends. The heat transfer effect of the evaporator can be fully exerted only when the capillary is operated under the design conditions. If the air volume of the evaporator is normal, it is found that the refrigerant flows through the evaporator according to the load change, preventing the formation of the frost tube. If the load is reduced, the liquid refrigerant will flow through the evaporator, and when it enters the suction pipe, the water vapor in the surrounding air will condense on the copper pipe. If there is enough liquid refrigerant, tube exposure will occur.

But it should be noted that when this method is used in a thermal expansion valve system, it will be found that the production of the exposed tube does not indicate the amount of refrigerant injected (even if an excessive amount of refrigerant is injected), because the expansion valve will automatically adjust the temperature.

7. Weigh the punch (this is the best method)

In fact, the weighing and filling method is the best method among the above methods, and it is suitable for any refrigeration system. The method is to weigh the refrigerant charged. As long as the manufacturer indicates the correct filling amount of the water-cooled cabinet or split machine on the nameplate. This method is the approved recommended filling method.

Note: When starting the equipment after a power failure for more than 12 hours, the crankcase heater must be energized and preheated. The purpose is to evaporate the liquid refrigerant mixed in the refrigerating oil in the crankcase to prevent the compressor from inhaling the liquid refrigerant. compression.

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