This is a BRAND NEW Carrier/Bryant/Payne Heat Pump Defrost Sensor! The Part # HH18HA280A (also HH18HA280) rated at L80-50. When a defrost sensor goes bad the heat pump will often turn to a solid block of ice. Thanks for looking and good luck!
Sensors detect events or changes in their environment, and then relay the information to another device, typically a control board.