IO HVAC Controls Suction Line Free Thermostat monitors the suction line temperature of an AC unit. The FS-38 acts as a thermostatic switch to prevent the AC coils from freezing. It also prevents potential water damage in the event of a blower motor failure, restricted airflow from a dirty filter, clogged coil or low refigerant. The stats open at 38 degrees Fahrenheit and close again at 50 degrees. Installation is effective and easy as the product easily snaps onto the suction line.