This freeze protection control is a low cost control designed to protect the air conditioning coil from freezing. The FPC is installed by simply snapping it onto the suction line just outside the evaporator coil. One wire lead of the FPC is connected to the "Y" terminal of your furnace or air handler, and the other to the "Y" terminal on your compressor. When the FPC senses temperature at 38 degrees it breaks the circuit to the compressor relay, preventing a freeze up. The FPC then remakes the compressor circuit at 48 degrees allowing ample time for the compressor to be off. This differential prevents short cycling. During the period the compressor is off the fan is still running using the cold coil to provide air conditioning.