Lennox 78W99 Limit Switch
The Lennox 78W99 Limit Switch is a critical safety component engineered to regulate heat exchanger temperatures within Lennox G40, G41, G50, G51, and G61 gas furnaces. This L235-30F thermal limit control features a fixed temperature setting, designed to open the electrical circuit at 235°F and automatically reset once temperatures drop by a 30°F differential. Precision-calibrated for high-limit protection, this SPST (Single Pole Single Throw) switch prevents the blower motor from circulating overheated air and protects the heat exchanger from cracks caused by excessive thermal stress. For contractors performing a furnace limit switch replacement, the 78W99 provides a direct OEM fit with standard 1/4-inch male spade terminals, ensuring a reliable interface with the integrated furnace control board. Utilizing genuine Lennox HVAC replacement parts maintains the UL listing and factory performance specifications of the heating system during peak demand cycles.
- Automatic Reset Functionality: Restores circuit continuity once the plenum temperature cools below the 205°F threshold.
- OEM Compatibility: Replaces Lennox part numbers 78W99, 78W9901, and 100582-13 without requiring bracket modifications.
- Critical Safety Protection: Mitigates fire hazards by interrupting the gas valve circuit if airflow is restricted or the inducer motor fails.
- Industrial Build Quality: Constructed with high-grade bimetallic discs to ensure accurate temperature sensing and longevity in high-temperature environments.
Common Technical Questions
What causes a Lennox furnace to trip the high limit switch?
Frequent tripping is usually indicative of restricted airflow, often caused by a clogged air filter, undersized ductwork, or a failing blower motor capacitor.
How do I test the Lennox 78W99 for continuity?
Set your multimeter to the ohms (?) setting; at room temperature, the L235-30F switch should show a closed circuit (0 ohms). If the circuit is open at room temperature, the switch has failed.
Is the 78W99 a universal HVAC limit switch?
No, this switch is specifically calibrated to the 235°F trip point required for Lennox residential furnaces. Using a switch with a different temperature rating can lead to premature heat exchanger failure or safety hazards.
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: $35.07
-65%$35.07
$12.27Lennox 78W99 Limit Switch
The Lennox 78W99 Limit Switch is a critical safety component engineered to regulate heat exchanger temperatures within Lennox G40, G41, G50, G51, and G61 gas furnaces. This L235-30F thermal limit control features a fixed temperature setting, designed to open the electrical circuit at 235°F and automatically reset once temperatures drop by a 30°F differential. Precision-calibrated for high-limit protection, this SPST (Single Pole Single Throw) switch prevents the blower motor from circulating overheated air and protects the heat exchanger from cracks caused by excessive thermal stress. For contractors performing a furnace limit switch replacement, the 78W99 provides a direct OEM fit with standard 1/4-inch male spade terminals, ensuring a reliable interface with the integrated furnace control board. Utilizing genuine Lennox HVAC replacement parts maintains the UL listing and factory performance specifications of the heating system during peak demand cycles.
- Automatic Reset Functionality: Restores circuit continuity once the plenum temperature cools below the 205°F threshold.
- OEM Compatibility: Replaces Lennox part numbers 78W99, 78W9901, and 100582-13 without requiring bracket modifications.
- Critical Safety Protection: Mitigates fire hazards by interrupting the gas valve circuit if airflow is restricted or the inducer motor fails.
- Industrial Build Quality: Constructed with high-grade bimetallic discs to ensure accurate temperature sensing and longevity in high-temperature environments.
Common Technical Questions
What causes a Lennox furnace to trip the high limit switch?
Frequent tripping is usually indicative of restricted airflow, often caused by a clogged air filter, undersized ductwork, or a failing blower motor capacitor.
How do I test the Lennox 78W99 for continuity?
Set your multimeter to the ohms (?) setting; at room temperature, the L235-30F switch should show a closed circuit (0 ohms). If the circuit is open at room temperature, the switch has failed.
Is the 78W99 a universal HVAC limit switch?
No, this switch is specifically calibrated to the 235°F trip point required for Lennox residential furnaces. Using a switch with a different temperature rating can lead to premature heat exchanger failure or safety hazards.
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 78W99 Limit Switch is a critical safety component engineered to regulate heat exchanger temperatures within Lennox G40, G41, G50, G51, and G61 gas furnaces. This L235-30F thermal limit control features a fixed temperature setting, designed to open the electrical circuit at 235°F and automatically reset once temperatures drop by a 30°F differential. Precision-calibrated for high-limit protection, this SPST (Single Pole Single Throw) switch prevents the blower motor from circulating overheated air and protects the heat exchanger from cracks caused by excessive thermal stress. For contractors performing a furnace limit switch replacement, the 78W99 provides a direct OEM fit with standard 1/4-inch male spade terminals, ensuring a reliable interface with the integrated furnace control board. Utilizing genuine Lennox HVAC replacement parts maintains the UL listing and factory performance specifications of the heating system during peak demand cycles.
- Automatic Reset Functionality: Restores circuit continuity once the plenum temperature cools below the 205°F threshold.
- OEM Compatibility: Replaces Lennox part numbers 78W99, 78W9901, and 100582-13 without requiring bracket modifications.
- Critical Safety Protection: Mitigates fire hazards by interrupting the gas valve circuit if airflow is restricted or the inducer motor fails.
- Industrial Build Quality: Constructed with high-grade bimetallic discs to ensure accurate temperature sensing and longevity in high-temperature environments.
Common Technical Questions
What causes a Lennox furnace to trip the high limit switch?
Frequent tripping is usually indicative of restricted airflow, often caused by a clogged air filter, undersized ductwork, or a failing blower motor capacitor.
How do I test the Lennox 78W99 for continuity?
Set your multimeter to the ohms (?) setting; at room temperature, the L235-30F switch should show a closed circuit (0 ohms). If the circuit is open at room temperature, the switch has failed.
Is the 78W99 a universal HVAC limit switch?
No, this switch is specifically calibrated to the 235°F trip point required for Lennox residential furnaces. Using a switch with a different temperature rating can lead to premature heat exchanger failure or safety hazards.
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.
