Lennox 73K21 Limit Switch
The Lennox 73K21 Limit Switch is a critical safety component designed for precise thermal regulation within residential gas furnaces and air handlers. Engineered as a Lennox replacement part, this 145-175F AUTO limit switch monitors discharge air temperatures to prevent heat exchanger overheating. It operates on a normally closed circuit that opens if temperatures exceed the 175°F threshold, effectively cutting power to the gas valve or ignition control. Once the system cools to the 145°F reset point, the switch automatically resets to restore unit operation. This HVAC high limit sensor features a standard flange mount for secure positioning within the plenum or blower housing, ensuring accurate sensing of thermal fluctuations. For technicians performing furnace limit switch troubleshooting, the 73K21 offers a direct-fit solution that maintains the original equipment manufacturer’s specifications for response time and mechanical reliability during high-cycle demands.
Key Benefits for Contractors- Direct OEM Compatibility: Engineered specifically for Lennox legacy and modern furnace platforms to ensure no-drill installation.
- Automatic Reset Functionality: Eliminates the need for manual intervention once the temperature drops to the 145°F differential.
- Rugged Bi-Metal Construction: Designed to withstand the high-heat environment of the heat exchanger without premature calibration drift.
- System Protection: Acts as a primary fail-safe against low airflow conditions caused by clogged filters or failed blower motors.
What causes the 73K21 limit switch to trip frequently?
Frequent tripping usually indicates restricted airflow, such as a secondary heat exchanger blockage or an undersized duct system, forcing the discharge air temperature above the 175°F limit.
Can this switch be used in non-Lennox equipment?
While the 145-175F range is standard for many furnace brands, the mounting flange and probe depth are specific to Lennox configurations; always verify physical dimensions before attempting cross-brand installation.
How do I verify if the switch is faulty?
Test for continuity across the terminals when the furnace is cold. If the circuit is open at room temperature, the internal bi-metal disc has failed or is stuck in the open position.
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.
Original: $10.62
-65%$10.62
$3.72Lennox 73K21 Limit Switch
The Lennox 73K21 Limit Switch is a critical safety component designed for precise thermal regulation within residential gas furnaces and air handlers. Engineered as a Lennox replacement part, this 145-175F AUTO limit switch monitors discharge air temperatures to prevent heat exchanger overheating. It operates on a normally closed circuit that opens if temperatures exceed the 175°F threshold, effectively cutting power to the gas valve or ignition control. Once the system cools to the 145°F reset point, the switch automatically resets to restore unit operation. This HVAC high limit sensor features a standard flange mount for secure positioning within the plenum or blower housing, ensuring accurate sensing of thermal fluctuations. For technicians performing furnace limit switch troubleshooting, the 73K21 offers a direct-fit solution that maintains the original equipment manufacturer’s specifications for response time and mechanical reliability during high-cycle demands.
Key Benefits for Contractors- Direct OEM Compatibility: Engineered specifically for Lennox legacy and modern furnace platforms to ensure no-drill installation.
- Automatic Reset Functionality: Eliminates the need for manual intervention once the temperature drops to the 145°F differential.
- Rugged Bi-Metal Construction: Designed to withstand the high-heat environment of the heat exchanger without premature calibration drift.
- System Protection: Acts as a primary fail-safe against low airflow conditions caused by clogged filters or failed blower motors.
What causes the 73K21 limit switch to trip frequently?
Frequent tripping usually indicates restricted airflow, such as a secondary heat exchanger blockage or an undersized duct system, forcing the discharge air temperature above the 175°F limit.
Can this switch be used in non-Lennox equipment?
While the 145-175F range is standard for many furnace brands, the mounting flange and probe depth are specific to Lennox configurations; always verify physical dimensions before attempting cross-brand installation.
How do I verify if the switch is faulty?
Test for continuity across the terminals when the furnace is cold. If the circuit is open at room temperature, the internal bi-metal disc has failed or is stuck in the open position.
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.
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Description
The Lennox 73K21 Limit Switch is a critical safety component designed for precise thermal regulation within residential gas furnaces and air handlers. Engineered as a Lennox replacement part, this 145-175F AUTO limit switch monitors discharge air temperatures to prevent heat exchanger overheating. It operates on a normally closed circuit that opens if temperatures exceed the 175°F threshold, effectively cutting power to the gas valve or ignition control. Once the system cools to the 145°F reset point, the switch automatically resets to restore unit operation. This HVAC high limit sensor features a standard flange mount for secure positioning within the plenum or blower housing, ensuring accurate sensing of thermal fluctuations. For technicians performing furnace limit switch troubleshooting, the 73K21 offers a direct-fit solution that maintains the original equipment manufacturer’s specifications for response time and mechanical reliability during high-cycle demands.
Key Benefits for Contractors- Direct OEM Compatibility: Engineered specifically for Lennox legacy and modern furnace platforms to ensure no-drill installation.
- Automatic Reset Functionality: Eliminates the need for manual intervention once the temperature drops to the 145°F differential.
- Rugged Bi-Metal Construction: Designed to withstand the high-heat environment of the heat exchanger without premature calibration drift.
- System Protection: Acts as a primary fail-safe against low airflow conditions caused by clogged filters or failed blower motors.
What causes the 73K21 limit switch to trip frequently?
Frequent tripping usually indicates restricted airflow, such as a secondary heat exchanger blockage or an undersized duct system, forcing the discharge air temperature above the 175°F limit.
Can this switch be used in non-Lennox equipment?
While the 145-175F range is standard for many furnace brands, the mounting flange and probe depth are specific to Lennox configurations; always verify physical dimensions before attempting cross-brand installation.
How do I verify if the switch is faulty?
Test for continuity across the terminals when the furnace is cold. If the circuit is open at room temperature, the internal bi-metal disc has failed or is stuck in the open position.
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.
