Procedure
1. Connect a pressure gauge to the air conditioning system to measure pressure.
2. Place a towel under the open end of the center hose.
3. Slowly open the high pressure valve and discharge the air conditioning system.
Warning! If the refrigerant in the air conditioning system is discharged quickly, compressor oil may leak out of the system.
4. Check if there are any oil stains on the towel. If so, close the valve slowly.
5. After the pressure in the air conditioning system decreases below 3.5 kg/cm², open the low pressure valve.
Information is copied from the website HyundaiBook
6. Open the high and low pressure valves and slowly reduce the pressure in the air conditioning system until the pressure gauge shows 0 kg/cm².