Johnson Controls A28AK-1 2-SPDT Flange Mounted Duct Temperature 30°F/110°F Differential 2F

The Johnson Controls A28AK-1 is a two-stage flange mounted duct thermostat designed to regulate air temperature within HVAC systems. It features a remote bulb sensor that detects air temperature within a duct and triggers two independent switches (SPDT) based on pre-set settings. When the air temperature rises above the desired level (adjustable between 30°F and 110°F), the A28AK-1 activates the first stage, typically turning on a cooling system. If the temperature continues to rise beyond a set differential (2°F in this case), the second stage activates, potentially engaging additional cooling or triggering an alarm. This dual-stage operation allows for efficient temperature control and prevents excessive cycling of HVAC equipment. The A28AK-1's flange mounting design makes for easy installation on air ducts, and its remote bulb sensor ensures accurate temperature reading from the air stream. This type of thermostat is commonly used in rooftop units, make-up air heaters, duct heaters, and various air handling systems.