What is the right pressure for refrigerant R-134 a in the air conditioning of automobiles and refrigerators?

We do not recommend that the gas charge in hermetic refrigeration systems be given on the basis of internal pressure. The gas charge must always be given through dosers or gas charging station. A gas doser has a gram scale where you can inject the exact amount of gas needed for each system. Each refrigerator model works with a specific amount of gas. Therefore, when applying a charge to a particular refrigerator, it is necessary to observe the quantity in grams of gas that is specified in the nameplate of the product. With respect to pressure in automotive air conditioning, the correct refrigerant charge is given by the amount of refrigerant in grams or kg. Only by pressure can not guarantee that the device is at full capacity, as there is a variation of pressure and yield for each car.