The Trol-A-Temp Freeze Protection Control, Model FPC, 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. When the FPC senses temperature at 38 deg it breaks the circuit to the compressor relay, preventing a freeze up. The FPC then remakes the compressor circuit at 48 deg allowing ample time for the compressor to be off. This-differential prevents any short cycling. During the period the compressor is off the fan is still running using the cold coil to provide air conditioning.
Honeywell Freeze Protection Control