Johnson Controls A28AA-4 2-SPDT Two-Stage Mechanical Space Temperature Control 30°F/110°F

The Johnson Controls A28AA-4 is a two-stage mechanical space temperature control used in heating ventilation and air conditioning (HVAC) systems to regulate temperature. This one has a remote bulb sensor that measures the temperature around it and turns on two individual switches (SPDT) to operate your HVAC appliances in two stages. This is a better method of controlling temperature as compared to single stage controls. The user then enters a preferred temperature range between 30°F and 110°F on the control. The remote bulb is always on and measures the space temperature. If the temperature drops below the set point the first stage is initiated which turns on your heating system such as the furnace.