A circular disk covered in rubber or plastic with a hole in the center where the edge is sometimes tensioned by a spring that prevents fluid from leaking at the Evaporator Case. A component which provides a Sealing surface at the HVAC Case. Heater Core Case Seal. Air Conditioning (A/C) Evaporator Core. Blower Assembly. Distribution box. Heater Core. Housing Assembly. HVAC Unit. Included with: AC & Heater Case.