What are the Cooling and Heating Pressures of an Air Conditioner? How to Calculate the Optimal Refrigerant Quantity?

During installation, if the outdoor unit of the air conditioner is higher than the indoor unit and the drop of the connecting pipe of the air conditioner is more than 10 meters, an oil return bend must be left every 6 meters. (The radius of the bend is about 30 cm)
Note: The above is for general cases. For specific models, please refer to the requirements in the technical service manual and the user manual.
After lengthening the connecting pipe during the installation of household air conditioners, the refrigerant must be filled strictly in accordance with the requirements on the nameplate or in the instruction manual. Under - filling, over - filling or leakage of the refrigerant will cause system failures!
Vacuum - pumping steps:
When the vacuum pump is placed horizontally, ensure that the lubricating oil is level with the oil level line. Check whether the rubber sealing gasket is damaged and whether the pointer of the pressure gauge points to zero.
Connect the refrigerant - charging tube, the pressure gauge and the vacuum pump together. Unscrew the nut at the refrigerant - charging port from the large valve, screw the refrigerant - charging tube onto the refrigerant - charging port, and confirm whether the thimble is in place.
First, open the valve of the pressure gauge, then turn on the power switch of the vacuum pump to start vacuum - pumping. During vacuum - pumping: Observe the pressure gauge (low - pressure). Stop vacuum - pumping when the pressure reaches about - 0.1 MPa (negative pressure). The vacuum - pumping time should be determined according to the model of the air conditioner and the size of the vacuum pump, and should be based on the pressure value shown on the pressure gauge.
First, close the valve of the pressure gauge, then turn off the power switch of the vacuum pump. Remove the refrigerant - charging tube from the vacuum pump, tighten the cap on the air inlet nozzle of the vacuum pump to prevent dust from entering. After vacuum - pumping, it is necessary to maintain negative pressure. For air conditioners above 2 horsepower, maintain the pressure for 5 minutes, and for air conditioners below 2 horsepower, maintain the pressure for 3 minutes.
Confirm that the pressure is not greater than about 0.08 MPa (a small rebound of 0.02 MPa in pressure is allowed) before proceeding with the subsequent processes; if the pressure is greater than about 0.08 MPa, it indicates a leak. Then, find the cause of the leak and solve it, and repeat the above processes.
After confirming that there are no leak points, open the valve core of the small valve. Close the small valve when the pressure (low - pressure) reaches 0.1 MPa - 0.5 MPa. If the pointer of the pressure gauge does not move at this time, slightly open the valve of the pressure gauge to check if there is gas discharging. If there is no gas discharging, it means that the connection between the refrigerant - charging tube and the air - conditioner valve is not in place, and the thimble of the refrigerant - charging tube has not opened the valve core of the valve. At this time, the vacuum - pumping operation should be carried out again.
After confirming that the vacuum - pumping operation is completed, then fully open the small valve and the large valve again, and remove the refrigerant - charging tube and the pressure gauge.
Basic knowledge of refrigerant filling:
R410A is an HFCs refrigerant composed of R32 and R125 in a mass fraction ratio of 1:1.
Compared with R22, the condensing pressure of R410A is approximately 1.6 times that of R22. It is a high - pressure refrigerant, and the pressure - bearing strength of the system needs to be increased.
Compared with R410A, the saturation pressure of R32 refrigerant is about 2.5% higher.
Precautions for refrigerant filling:
R22 and R410A have different components and pressures, and the thickness of the copper pipes of the machines is also different. Therefore, the two refrigerants are prohibited from being mixed. The measuring instruments and refrigerant - charging equipment for maintenance should also be dedicated.
After lengthening the connecting pipe, the refrigerant must be filled strictly in accordance with the requirements on the nameplate or in the instruction manual. Under - filling or leakage of the refrigerant will cause system failures!
The refrigerant volume for the lengthened pipes of different brands of air conditioners is slightly different. This table is for reference only!
Steps for refrigerant filling:
Connect the joint on the side of the vacuum pump during vacuum - pumping to the refrigerant tank and tighten it; open the switch of the refrigerant tank by 1/10 turn.

After the gas sprays out from the hose connected to the pressure gauge for 3 seconds, tighten the hose thread; (evacuate the gas inside the connecting pipe) open the pressure gauge and the switch of the refrigerant tank (be careful not to open it too wide to avoid liquid hammering).
Control the opening degree of the refrigerant tank and fill the refrigerant according to the pressure comparison table; after closing the pressure - gauge switch tightly after filling the refrigerant, wait for 5 minutes. If the pressure and current values are still low, add a small amount of refrigerant and observe until the pressure and current meet the requirements of the comparison table.
After filling, close the switch of the refrigerant tank tightly, quickly remove the pressure - gauge hose from the large valve, install the back - cover nut and the refrigerant - injection nozzle nut, and tighten them with a wrench.
Common after - sales problems:
Refrigerant is not added after lengthening the connecting pipe.
During the repair process, when the compressor is found to be broken, instead of finding the problem, the compressor is directly replaced, resulting in the damage of multiple compressors.