Abstract: An air conditioning system includes a compressor which is reversed in order to switch from a heating mode to a defrost mode, or in order to switch between heating and cooling modes. Prior to being reversed, the compressor is automatically reduced to a slower speed greater than zero for a predetermined time period to minimize damage and noise when reversal occurs. The compressor is reversed while at the slower speed when switching the system to a defrost mode. When switching between heating and cooling modes, the compressor speed is first reduced to the slower speed for the first predetermined time period and then to zero speed for a second predetermined time period, before the compressor is reversed.