Johnson Controls A28AA-28 2-Stage Temperature Control 30° To 110°F 6" Capillary 12" Adjustable Averaging Bulb

The Johnson Controls A28AA-28 is a two stage temperature control that is named as 2SC28A in electronics field and is widely used in heating and cooling systems (HVAC). This has a remote bulb sensor with a long capillary tube which can be positioned anywhere conveniently. Temperature changes are sensed and two independent electrical switches are activated by two different setpoints and differential. The 12- averaging bulb measures the average temperature of a particular zone and sends the data through the 6-foot capillary tube to the control unit. When the temperature gets to the first stage set point, the A28AA-28 turns on the first switch which usually controls a low capacity cooling or heating stage.