The performance of automotive A/C system depends on the correct refrigerant charge level. The under-charged or over-charged A/C system will have adverse effects on the system performance. If the system is undercharged initially or due to inevitable minute leaks from the system, the amount of refrigerant charge level will decrease over a period time and ultimately reduce the system's performance. Excessive charge beyond the optimum level will increase the pressure of refrigerant at condenser and TXV outlet and beyond optimum charge level there is no improvement on airside performance of A/C system. This research work presents the methodology for determination of optimum charge level for a desired amount of superheat and subcooling of refrigerant in an automotive A/C system under steady state conditions. Oil concentration in refrigerant is also precisely recorded and is found to be 4.17% which is below the tolerable limit. In the present study superheating between 5-12K and subcooling up to 10K is considered as per the historical data available with manufacturer. The optimum charge quantity is decided by adding the minimum value of the subcooling period and 2/3rd of the band width of subcooling graph. The set of experiments have been conducted in a sophisticate, highly precise and state-of-the-art system test bench/calorimeter on vehicle HVAC system and the system accuracy that determines the optimum charge quantity is ± 3.37%.