An experimental study was conducted on the effects of the amount of working fluid on the performance of a two-row copper-R134a heat pipe heat exchanger at the air side. The heat pipe heat exchanger operates in the horizontal configuration, and five different fluid charges were studied to cover the underload and overload cases. Moreover, the calculated outlet temperature of the evaporator side, obtained from the heat exchanger simulation, was compared with the experimental results. Based on the present study, it was found that the optimum performance of the copper-R134a heat pipe heat exchanger can be achieved at a fluid charge slightly exceeding the amount required to saturate the wick.