Johnson Controls A28AA-4 Temperature Control

The Johnson Controls A28AA-4 is a heavy-duty two-stage temperature control designed for versatile HVAC applications requiring sequenced switching. This electro-mechanical thermostat features dual SPDT switch action, allowing for precise control over two separate circuits based on temperature fluctuations. With a wide 30 to 110 degree setpoint range and a multi-voltage capacity of 120/208/240/277 Vac, it is a standard component for commercial cooling and heating systems. The unit utilizes a 1 3/8" x 2 1/4" coiled bulb for efficient thermal response and a convertible range adjuster for field flexibility. Maintenance and installation are streamlined as the A28AA-4 is identical to A28AA-4C. Technicians rely on the 3 1/2 degree differential per stage and the 3 degree fixed differential between stages to prevent short-cycling. This industrial temperature controller ensures reliable load management for compressors and fans in commercial refrigeration and ventilation setups.

• Dual Stage Sequencing: Features two SPDT switches to manage multiple loads or stages of heating and cooling effectively.
• Electrical Versatility: Operates across 120/208/240/277 Vac, making it compatible with various building automation systems.
• Precise Differentials: Maintains a 3 1/2 degree differential for each stage with a 3 degree fixed inter-stage differential for stable ambient temperature control.
• Installation Flexibility: Includes a convertible range adjuster for customized setpoint configuration in the field.

Common Questions

What is the difference between the A28AA-4 and the A28AA-4C?
These two models are functionally identical and share the same technical specifications, allowing for direct replacement in existing systems.

How do I wire the Johnson Controls A28AA-4 for cooling applications?
Since this unit features 2 SPDT switches, you must identify the common, normally open (NO), and normally closed (NC) terminals to ensure the circuit closes upon a temperature rise for cooling stages.

Can this unit be used in high-voltage industrial HVAC setups?
Yes, the A28AA-4 controller is rated for up to 277 Vac, making it suitable for standard industrial and commercial line voltage applications.

Disclaimer: While we strive for 100% accuracy, product data and specifications are subject to change. Please contact our team to confirm compatibility or technical details before purchasing.