The UMM-FS monitors the suction line temperature through a FS-38 Freeze Stat to prevent coil freeze up. If the suction line temperature falls below 38 degrees F, the monitor will open a set of dry contacts breaking the Y wire to the compressor. The built-in differential of the freezed stat also prevents short cycling of the compressor. iO HVAC UMM-FS Universal Malfunction Monitor with Freeze Stat