The CO2-4e has four timers that are used to control your CO2.to add just the right amount of CO2 without the wasteful "overshoot" that other controllers have. One timer controls the length of time the CO2 is released and another controls how often the CO2 is released. The result is a very efficient method of controlling CO2. The "Overall Cycle timer" allows the user to decide how long the supplemental CO2 is kept in the growing area prior to being exhausted. When the "Overall Cycle" time expires, the CO2-4e turns ON the exhaust outlets and enables the "Exhaust Cycle Timer", which controls the amount of time the exhaust fans will run. When complete, the cycle is reset and the CO2 cycle starts again. It also features temperature and humidity controls which will disable CO2 injection if the temperature or humidity levels that you specify are exceeded, activating an exhaust outlet which can control ventilation equipment (air conditioner, fan, etc.) It also has a built in photo controller, which disables the CO2 function when the lights are off. The CO2-4e can also be used with the PPM-1c sensor for unequalled Parts-Per-Million performance. The CO2-4e is rated for 15 amps @ 120 volts.