Honeywell T678A1437 Controller

The Honeywell T678A1437 is a heavy-duty remote bulb controller designed for precise two-stage temperature control in commercial HVACR applications. As a veteran-grade mechanical thermostat, it excels in regulating temperatures within ducts, pipes, tanks, and boilers. This model features dual SPDT switch outputs that operate in sequence, making it the standard choice for staging dampers, valves, or multi-stage heating and cooling equipment. With a 0-100°F setpoint range and a 5-foot copper capillary, the T678A1437/U offers versatile mounting and reliable sensing for liquid or air mediums. The unit supports 120Vac, 240Vac, or 277Vac electrical configurations, providing the flexibility needed for diverse field installations. The fixed 3°F differential ensures stable cycling, while the 3-10°F interstage differential allows for fine-tuned sequencing of staged loads. Built for durability, the 1/2" x 4 3/16" sensing bulb handles a maximum operating temperature of 125°F, delivering rugged performance in demanding environments.

Key Benefits

• Dual-Stage Sequencing: Two independent SPDT switches allow for seamless staging of balanced HVAC loads.
• Versatile Application: Universal sensing capability for air, water, or oil in tanks, boilers, and industrial ductwork.
• Broad Voltage Compatibility: Field-selectable wiring for 120V, 240V, or 277V systems streamlines inventory for service contractors.
• Rugged Construction: Features a durable copper bulb and capillary designed to withstand high-vibration and industrial settings.
• Flexible Installation: The controller body can be mounted in any orientation without affecting calibration or performance.

Common Questions

Is the T678A1437 a direct replacement for the T675A?
While they look similar, the T678A1437 provides two-stage control (2 SPDT), whereas the T675A series typically provides single-stage control. Always check your wiring diagram to ensure multi-stage support.

Can this bulb be immersed directly in liquid?
Yes, the copper bulb is designed for immersion sensing in tanks and pipes. For high-pressure applications, the use of a well (immersion sleeve) is recommended to protect the capillary.

What is the difference between the T678A1437 and the T678A1437/U?
There is no functional difference; the "/U" suffix simply denotes a universal-packaged TRADELINE model, which often includes additional mounting hardware or cross-reference guides.

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.