An experimental study using a psychrometric calorimeter was conducted to investigate the temperature and pressure mea surement errors permitted for determining cooling capacity of an air conditioner. First, the instrument calibration was made in accordance with the related test methods and guidelines in order to accurately evaluate basic performance (cooling capacity and airs flow rate). Secondly, a parametric study was performed to examine the effect of measurement error involved if temperature and pressure measuring instruments on the cooling capacity calculation. From the results, it was found that the degree of accuracy for both temperature and pressure measurements played an important role on the error occurring in the determination of cooling capacity and needed to be maintained within a certain value to guarantee required accuracy of cooling capacity