Reznor 57953 Limit Switch

Ensure your commercial heating units operate within safe thermal parameters with the Reznor 57953 Limit Switch. This L170-40F limit control is a precision-engineered OEM replacement part designed to monitor discharge air temperatures and prevent heat exchanger damage. In the field, reliability is paramount; this switch features a fixed 170°F trip point and a 130°F reset differential (40°F drop), making it a critical safety component for Reznor gas-fired heaters and packaged systems like the RGBL, RPBL, and PGBL series. As a high-limit switch, it provides essential circuit interruption at the limit control level to protect against blower failure or restricted airflow. For technicians servicing high-output equipment, the Reznor 57953 ensures the system remains compliant with manufacturer specifications, maintaining the integrity of the HVAC temperature control loop without the risk of nuisance tripping or safety bypasses.

• Precise Thermal Calibration: Factory-set L170-40F rating ensures the Reznor 57953 trips at exactly 170°F to protect the heat exchanger.
• OEM Compatibility: Specifically engineered for Reznor 400, 500, 600, and 800 MBH units, ensuring a direct mechanical and electrical fit.
• Automatic Reset Function: Features a 40°F differential, allowing the system to safely re-engage once temperatures drop to 130°F.
• Durable Construction: Built to withstand the high-cycle demands of industrial gas furnace environments and air handling units.

What are the symptoms of a failing Reznor 57953 limit switch?
A faulty switch typically causes the furnace to "limit out," where the burners shut off prematurely while the blower continues to run. This often indicates the switch has either tripped due to an actual overheat condition (like a dirty filter) or the internal bimetal disc has failed and no longer maintains continuity.

Is the L170-40F switch interchangeable with other ratings?
No. For safety and compliance, you must use the Reznor 57953 or an exact L170-40F equivalent. Replacing it with a higher temperature limit can lead to cracked heat exchangers or fire hazards, while a lower limit will cause constant equipment short-cycling.

How do I test the 57953 limit control in the field?
With the power off, use a multimeter to check for continuity across the terminals. Since this is a "normally closed" (NC) switch, it should show 0 ohms at room temperature. If the circuit is open while the unit is cool, the switch is defective and requires immediate replacement.

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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.