Abstract: An energy saving controller for an air conditioning system comprising a temperature sensor or sensing and measuring the temperature in an area to be controlled, a memory device for storing a first set and a second set of reference temperatures, each set of reference temperatures including a heating reference temperature and a cooling reference temperature, and a controller in communication with the memory device for selecting one of the first and second sets of reference temperatures in the memory and for comparing the selected set of reference temperatures to the measured temperature of the area. The controller is adapted to select one set of reference temperatures when the area is unoccupied by a person and to select the other set of reference temperatures when the area is occupied by a person. The occupancy information is provided to the controller by an occupancy detector. A system switch is provided that communicates with the controller and selects between a heating mode, a cooling mode, and an off mode.