The Rheem-Ruud PD476604 Defrost & Ambient Sensor Kit is a replacement monitoring component designed for compatible heat pump HVAC systems. It works by measuring outdoor ambient and coil temperatures and sending data to the control board, allowing the system to initiate and terminate defrost cycles when needed. This helps prevent excessive frost buildup on the outdoor coil while mainta... https://www.partshnc.com/pd476604-rheem-ruud-defrost-and-ambient-sensor-kit