The Greenheck-manufactured Fenwal 35-615922-125 24Vac Dsi Module is a vital part of many HVAC systems. Its main duty is to precisely measure the differences in air pressure within ducting. In the event that predetermined parameters are exceeded, the module reacts quickly by turning on alarms or modifying dampers to bring the system back into balance. #Fenwal #35-615922-125 #ModuleG... https://www.partshnc.com/35-615922-125-fenwal-24vac-dsi-module-greenheck