The external AC booster is utilized by some owners as an additional option to regulate the temperature inside the cabin during use. When the chamber fully pressurizes the temperature in the cabin is about 76 degrees. If you prefer a cooler temperature, adding the external AC booster will regulate the temperature at lower settings of 68-75 degrees. The cabin oxygen exchange system that comes standard with all chambers already circulates pure oxygen into the chamber without the AC booster. The AC booster is simply to lower cabin temps if so desired lower than 76 degrees, it is not required to operate the system. The AC booster is an add-on feature.