The 5D51-90 Fan & Limit Control (White-Rodgers / Copeland Comfort Control) is a combination furnace control designed to manage blower fan operation and provide high-temperature safety protection in residential and light commercial heating systems. Featuring an 8-inch sensing element, this control automatically starts and stops the blower based on plenum temperature while protecting the furnace from overheating through its integrated limit switch function.

Cross-Reference

• 5D51-90
• 5D5190
• White-Rodgers 5D51-90
• Copeland Comfort Control 5D51-90

Direct OEM

White-Rodgers 5D51-90

Compatible Brands

• White-Rodgers
• Emerson
• Copeland
• York
• Coleman
• Luxaire
• Goodman
• Rheem
• Universal Warm Air Furnace Applications

Application

Used in forced-air furnaces to:

• Control blower fan operation
• Provide furnace high-limit protection
• Prevent circulation of cold air at startup
• Protect heat exchangers from overheating
• Automatically cycle the blower during heating operation
• Maintain proper furnace operating temperatures

Related Components

• Fan & Limit Control
• High Limit Switch
• Fan Switch
• Furnace Control Board
• Blower Relay
• Blower Motor
• Transformer
• Thermostat
• Plenum Temperature Control

Technician Notes

The 5D51-90 is a combination fan and limit control equipped with an 8-inch sensing element for applications requiring deeper insertion into the furnace plenum. This control combines blower fan management and overtemperature protection in a single device, reducing component count and simplifying service.

Before replacement, verify insertion length, mounting dimensions, temperature settings, and electrical ratings match the original control.

Common Symptoms of Failure

• Blower fan runs continuously
• Blower fails to start
• Furnace overheats
• High-limit shutdowns
• Short cycling
• Delayed blower operation
• Inconsistent heating performance
• Excessive furnace temperatures
• No heat output

Installation Tips

1. Disconnect power before servicing.
2. Label all wiring before removal.
3. Verify the 8-inch insertion length matches the original control.
4. Fully insert the sensing element into the plenum.
5. Inspect terminals for corrosion or overheating.
6. Verify blower motor operation and amperage.
7. Check fan and limit settings after installation.
8. Run the furnace through a complete heating cycle.

Recommended Inspection Items

• Blower motor condition
• Air filter restriction
• Heat exchanger temperature rise
• Blower relay operation
• Wiring terminals
• Furnace control board
• Supply and return airflow
• Venting system
• Blower wheel cleanliness