Is Vacuuming Necessary When Adding Refrigerant to a Car's Air Conditioning System?
2 Answers
Vacuuming is not necessary when adding refrigerant to a car's air conditioning system. Freon is used as a refrigerant in the air conditioning system, and its purpose is to absorb heat through compression by the compressor to achieve cooling. The method for adding Freon to a car is as follows: 1. Connect the manifold pressure gauge to the compressor and the refrigerant tank; 2. Open the refrigerant tank, loosen the nut on the middle injection hose, and after hearing the sound of refrigerant vapor flowing, tighten the nut to expel air from the hose; 3. Open the low-pressure manual valve to allow refrigerant to enter the cooling system, and close the manual valve when the pressure reaches 0.4 MPa; 4. Start the engine and turn on the air conditioning, set the fan speed and temperature to high, open the manual valve on the manifold pressure gauge, and allow the refrigerant to continue entering the cooling system until it reaches the specified value of 1.37 to 1.67 MPa.
Having worked in auto repair shops for many years, I always emphasize to apprentices that vacuuming is absolutely necessary before adding refrigerant. Skipping this step means residual air and moisture in the AC system will drastically reduce cooling efficiency. Moisture can also freeze in the pipes, causing blockages, and worse, lead to refrigerant degradation and compressor corrosion. The proper procedure is to connect a vacuum pump and continuously evacuate for about half an hour until the pressure gauge stabilizes at -30 inches of mercury. This step also incidentally checks for leaks in the system. If you skip this step to save time, the AC will soon have issues again, and the repair rate will skyrocket. That's why professional repairs treat this as an ironclad rule.
