Honeywell T678A1361 Contorller

The Honeywell T678A1361 Remote Bulb Controller is a heavy-duty industrial thermostat designed for regulating the temperature of air or liquids in ducts, pipes, tanks, and boilers. This dual-stage temperature controller features a wide 55°F to 175°F setpoint range and is a direct replacement for the HH29AA080 and T478A1002. Built with two SPDT output relays, it allows for seamless multi-stage control of heating, cooling, or dual-purpose HVACR systems. The unit utilizes a copper sensing bulb measuring 1/2" x 3-9/16" connected by a 20-foot capillary, providing the flexibility needed for remote mounting while maintaining high accuracy. With ambient temperature compensation, the controller ensures stable operation even when the case is exposed to fluctuating mechanical room conditions. It supports multiple voltages, including 120V, 240V, and 277V AC, and is engineered for versatile field installation in any mounting orientation.

Key Benefits for Contractors

• Direct Cross-Reference: Serves as the standard replacement for legacy HH29AA080 and T478A1002 controllers, reducing truck stock requirements.
• Multi-Voltage Compatibility: Universal power input supports 120Vac, 240Vac, or 277Vac, making it suitable for varied commercial electrical layouts.
• Precision Sequencing: Features a 3.6°F fixed differential with an adjustable 3.6° to 12°F interstage differential for fine-tuned equipment cycling.
• Industrial Durability: Rated for a maximum operating temperature of 200°F at the sensing bulb, ideal for high-limit boiler or tank applications.
• Flexible Installation: The 20' capillary length allows the sensing bulb to be positioned deep within ducts or fluid lines while the controller remains accessible.

Common Questions

Can this controller be used for both heating and cooling simultaneously?
Yes. Because it uses two SPDT (Single Pole Double Throw) relays, you can wire one stage for heating and the second for cooling, or use them to sequence two stages of the same heating or cooling source.

Is this unit suitable for mounting inside an air handler?
The T678A1361 is ambient compensated, meaning it provides accurate sensing at the remote bulb regardless of the temperature surrounding the controller housing itself, provided the ambient temp stays within specified limits.

What is the maximum load the relays can handle?
The contacts are designed for heavy-duty use with a maximum connected load of 2000 VA, allowing it to pilot high-amperage contactors or directly control smaller valves and motors.

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.