Rheem-Ruud 47-21711-08 Limit Switch

The Rheem-Ruud 47-21711-08 Limit Switch is a critical safety component designed for precise thermal regulation in Rheem furnace and HVAC applications. This OE OEM replacement part features a fixed open temperature of 130 degrees F and a fixed close temperature of 110 degrees F, ensuring reliable HVAC temperature control by breaking the circuit if internal temperatures exceed safety margins. Engineered as a SPST normally closed switch, it includes an auto reset function that automatically re-establishes the circuit once the system cools to the 110-degree differential, preventing nuisance lockouts while maintaining equipment protection. With a 7-inch insertion length, this board mounted limit switch provides accurate furnace plenum temperature sensing. For professional contractors, utilizing this genuine high-limit safety switch is essential for maintaining factory specifications and ensuring long-term system diagnostic stability. It serves as a direct replacement for various legacy Rheem and Ruud temperature controls used in residential and commercial air handlers.

• Precise Thermal Safety: Fixed 130°F trip and 110°F reset thresholds provide reliable protection against overheating.
• OEM Compatibility: Authentic Rheem-Ruud replacement part ensures exact fitment and electrical compliance for specific unit serial numbers.
• Efficient Installation: 7-inch probe length and board-mount configuration allow for fast field replacement in compatible furnace plenums.
• Automatic Recovery: The auto reset mechanism minimizes service calls after temporary overheating events.
• Industrial-Grade Build: Single Pole Single Throw (SPST) normally closed design handles standard control circuit loads without failure.

What causes a limit switch like the 47-21711-08 to trip frequently?
Frequent tripping is usually indicative of restricted airflow. Technicians should inspect for dirty air filters, blocked return grilles, or a failing blower motor. If the switch opens at 130°F, it is functioning as intended to protect the heat exchanger.

Can this 7-inch limit switch be used in applications requiring a shorter probe?
No, probe length is critical for accurate temperature sensing. Using a longer or shorter probe than the original specification can lead to delayed responses or premature tripping, potentially compromising system safety.

How do I verify if the auto reset is failing?
If the switch remains open (no continuity) after the plenum has cooled below 110°F, the internal bimetal disc is likely fatigued or damaged, necessitating a full replacement of the component.

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.