Johnson Controls A28AA-29 Temperature Control

The Johnson Controls A28AA-29 is a heavy-duty two-stage temperature control designed for precise cycling of multiple HVACR components. Featuring 2 SPDT switch action, this mechanical thermostat allows for sequenced control of heating, cooling, or ventilation equipment across a broad -30 to 100 degree setpoint range. For technicians replacing legacy components, the A28AA-29 serves as the direct Johnson Controls A28AA-81 replacement, maintaining exact mounting and wiring compatibility. The unit utilizes a 3/8" x 4" bulb and an 8' capillary length for flexible remote sensing in medium-temperature applications. It supports multi-tap voltage requirements, including 120/208/240/277 Vac, making it a versatile stock item for service trucks. With a fixed 5-degree temperature differential per stage and an adjustable differential between stages of 2 to 7 degrees, this controller prevents short-cycling while ensuring tight load management. The convertible range adjuster allows for easy setpoint modification in the field to meet specific site requirements.

Technical Benefits for Contractors

• Dual Stage Sequencing: Ideal for controlling multi-stage compressors or managing fan and compressor delay cycles.
• Wide Voltage Compatibility: Facilitates installation on multiple line voltages without the need for additional transformers.
• Remote Sensing Capability: An 8-foot copper capillary enables accurate temperature monitoring away from the control mounting location.
• Field-Proven Reliability: The robust vapor-tension sensing element provides consistent HVAC temperature control in demanding environments.
• Simplified Retrofitting: Built-in convertible range adjuster permits easy transition from internal adjustment to external knob control.

Common Technical Questions

What is the difference between A28AA-29 and A28AA-81?
The A28AA-29 is the current production model and is functionally identical to the discontinued A28AA-81, offering the same two-stage thermostat logic and footprint.

How do I adjust the staging interval?
The inter-stage differential is field-adjustable between 2 and 7 degrees Fahrenheit, allowing the technician to calibrate exactly when the second stage engages relative to the first.

Can this be used for both heating and cooling?
Yes, the SPDT switch action provides contacts that can be wired to open or close on temperature rise, supporting Johnson Controls temperature control configurations for either application.

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.