White-Rodgers 5D51-78 Control

The White-Rodgers 5D51-78 is a high-performance universal fan and limit control engineered for forced warm air heating systems. This unit features a 11-inch element with a helical bimetal sensor, making it the ideal choice for plenum installations with narrow space limitations. As a SPDT control, it effectively regulates fan or blower cycling while providing a critical high-limit safety cutoff. The fan switch operates on a close-on-rise action with an adjustable range of 50°F to 265°F, allowing technicians to fine-tune cut-in and cut-out setpoints using individual pointers on the face dial. The limit switch is factory-calibrated for an open-on-rise action between 100°F to 300°F with a 25°F fixed differential. For multi-voltage applications, the 5D51-78 includes a removable solid copper jumper between the fan and limit circuits, supporting line voltage, low voltage, or millivolt systems. A built-in summer fan switch allows for manual blower operation for seasonal ventilation without altering the primary temperature settings.

• Universal Compatibility: Includes a breakaway jumper for flexible wiring in millivolt or line voltage configurations.
• Compact Design: A single element type specifically designed for tight plenums and restrictive enclosures.
• Field Adjustability: Adjustable fan differential and limit stop settings provide precise control over furnace blower timing.
• Simplified Installation: Features slotted mounting holes and long terminal screws to facilitate fast wiring within the terminal block.
• Dual Functionality: Combines independent fan and limit mechanisms into a single standard size enclosure.

How do I set the fan cut-in and cut-out temperatures?
Use the individual pointers on the dial to set the "Fan On" (cut-in) and "Fan Off" (cut-out) temperatures. Ensure the differential is sufficient to prevent short-cycling of the blower motor.

Can the 5D51-78 be used in low voltage circuits?
Yes. To use the limit switch in a low voltage or millivolt circuit, the factory-installed line voltage jumper must be removed.

What is the purpose of the summer fan switch?
The manual lever allows the contractor or end-user to run the fan continuously for air circulation during warmer months without disturbing the automated heating setpoints.

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.