This study focuses on the effect of outdoor coil fan speed on the performance variation of the heat pump system by adopting the hot gas bypass method, and on the performance improvement with hot gas bypassing using the time step method to defrost. Tests were conducted for fan speeds 90, 60 and 30% of the normal speed of the outdoor coil together with the stationary case. Performance of the heat pump is compared with the conventional time step defrosting method for coefficient of performance (COP) and total heat capacity. Results show that the integrated heating capacity with hot gas bypassing is highest at 60% (780 rpm) of the fan speed and is 8.6% higher than that of the time step defrosting method. The averaged COP of the heat pump in this case is higher by 3.8% than the time step defrosting method and 2.8% higher than that of the stationary fan.