A blower motor assembly having a variable speed motor that is suitable for direct, drop-in replacement in a residential HVAC (heating, ventilation, and air conditioning) system that employs a PSC motor. The blower motor assembly includes at least a neutral input and two hot AC line connections, one for connection to the heating power source and the other to the cooling power source. A sensing circuit senses which of the inputs is energized by sensing either voltage or current on the inputs. The sensing circuit delivers a corresponding signal to a motor controller to control the speed of the variable speed motor. The blower motor assembly may also be equipped with additional hot AC inputs, more than one neutral line, and several sensing circuits for sensing current or voltage in the hot inputs and/or the neutral lines for controlling various aspects of the variable speed motor.