The recent incident in Gurgaon where two AC technicians were killed while servicing AC is a reminder to be extra careful especially while refilling gas.
Besides, it is also important to know that air conditioner refrigerant is toxic.
Amongst the first safety measures required is to wear gloves and protective eyeglasses.
The use of proper tools is equally important
While you unscrew the bolt of the suction line remember to loosen the screw inside with a Torx hex key. Then remove all air from the system as any moisture inside the compressor may lead to its damage.
Also ensure that all the valves of the AC manifold gauge are closed.
After carefully following all the above mentioned steps open the low side knob of the manifold for 3-4 seconds and close it. Thereafter switch on the AC and wait till the compressor starts.
Once the compressor is operational once again again open the low side valve of the manifold. Keep the valve opened for 4 seconds and close it for 2 seconds. Note the pressure on the gauge when the valve is closed. Keep doing it till the pressure settles between 60-70 PSI.
Remember that the AC refrigerant gas is filled in small amounts because releasing all the gas at once will damage the compressor.
Once the pressure reaches 60-70 PSI range close the manifold valve and the refrigerant tank knob. Disconnect the refrigerant tank.
Follow the above steps and be safe. Live long.