McDonnell & Miller 309000 Resistor Kit

The McDonnell & Miller 309000 Resistor Kit, specifically the Model 7B-1R, is a critical slide wire resistor assembly engineered for proportional signal control in industrial boiler systems. This 135-ohm resistor kit is designed to interface directly with 7B switches, providing the necessary modulating signal for precise burner control and water level management. As a veteran-grade replacement part, it is compatible with the Series 93, Series 193, Series 94, and Series 194 combination low water cut-off (LWCO) and pump controllers. The kit now incorporates the SA7-3 slide wire component, ensuring a smooth resistive sweep and reliable feedback loop communication. High-grade construction allows this HVACR control component to maintain calibration accuracy under the thermal stress common in steam boiler applications. For contractors performing field repairs on proportioning controls, this OEM resistor assembly is the standard for restoring system automation and proportional firing sequences.

Key Benefits:

• Ensures accurate 135-ohm proportional signaling for consistent modulating burner performance.
• Direct OEM replacement for 7B switch assemblies on legacy and modern McDonnell & Miller controllers.
• Includes the updated SA7-3 slide wire kit, improving signal stability and hardware longevity.
• Compatible with a wide range of industrial units, including Series 93 and Series 194 pump controllers.
• Rugged slide wire design facilitates easier field calibration and deadband adjustment.

Common Questions:

What is the primary resistance value for the 7B-1R kit?
The McDonnell & Miller 309000 is a 135-ohm resistor essential for the proportional control signal required by standard HVACR modulation motors.

Which boiler controllers are compatible with this resistor?
This slide wire resistor kit is specifically designed for Series 93, 94, 193, and 194 combination low water cut-offs and pump controllers utilizing a 7B switch.

Is the slide wire included in this assembly?
Yes, the Model 7B-1R now includes the SA7-3 slide wire kit as part of the 309000 part number for a complete switch repair solution.

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.