It bypasses warm air throughout the ACM when opened. The air is introduced in to the expansion ducting, just upstream on the h2o separator, where it heats the air just enough to help keep it from freezing. Thus, the refrigeration bypass valve regulates the temperature with the ACM discharge air http://elliotlsujq.imblogs.net/12152720/how-air-conditioning-can-save-you-time-stress-and-money