While the CT-DH-3 has many applications, it was primarily developed for use with CO2 equipment and exhaust/ventilation fans. The left side (or equipment) outlets of the controller are normally "ON" until defeated when the right side outlets are activated. Internal sensor will allow for 7ºF temperature zone and a 5% humidity differential between the time that the fans come "ON" and then turn "OFF" again. When temperature or humidity rises above your dial set points, the right outlets will activate and the left outlets will deactivate. The right side outlets will remain “ON” until the temperature drops 7º and/or the humidity drops 5% below your set points. At which time, the right outlets will shut “OFF” and reactivate the left outlets.