Abstract: A diffuser cartridge (10) of restricted height is provided for controlling flow of air in an air conditioning system. The cartridge (10) has two axially aligned temperature sensitive elements (34,68) for respectively sensing room temperature and duct temperature variations. Arms (12) are provided for displacing an air flow baffle (B) and a control structure is provided for displacing the arms (12) in response to sensed room and duct temperatures. The control structure pivots the arms (12) cam-fashion as it is moved vertically by the temperature sensitive elements (34, 68). The control structure has two springs (54,56) that act in series to counter movement of the control structure by the temperature sensitive elements (34,68). The springs (54,56) are nested coaxially within each other, with an intermediate component (48) transferring compressive loads from one spring to the other.