The S1-025-35381-000 Auto Limit Switch is a temperature-sensitive safety control designed to protect furnaces and air handlers from overheating. This automatic reset limit switch opens at 145°F and resets at 115°F, interrupting the control circuit when excessive temperatures are detected and automatically restoring operation once safe temperatures return. Commonly used in residential and light commercial HVAC equipment to safeguard heat exchangers, blower compartments, and critical heating components.

Cross-Reference

• S1-025-35381-000
• 025-35381-000

• 3L01-180
• York S1-025-35381-000
• Source 1 S1-025-35381-000

Direct OEM

• Source 1
• York
• Johnson Controls

Compatible Brands

• York
• Coleman
• Evcon
• Luxaire
• Fraser-Johnston
• Guardian
• Air Pro
• Johnson Controls equipment

Application

• Furnace high-limit protection
• Heat exchanger temperature monitoring
• Blower compartment over-temperature protection
• Gas furnace safety circuits
• HVAC heating system safety controls
• OEM limit switch replacement

Related Components

• Flame sensors
• Rollout switches
• Pressure switches
• Control boards
• Ignition modules
• Blower motors
• Fan relays
• Furnace door switches
• Temperature safety controls

Technician Notes

• Automatic reset design restores operation after temperatures return to acceptable levels.
• Opens at 145°F and automatically resets at 115°F.
• Designed to protect furnace components from overheating damage.
• Frequent limit trips typically indicate airflow restrictions or blower performance issues.
• Verify mounting surface provides accurate temperature sensing.
• Always investigate root cause before replacing the limit switch.

Common Symptoms of Failure

• Furnace shuts down on limit
• Intermittent heating operation
• Short heating cycles
• No heat condition
• Blower runs continuously
• Repeated high-limit trips
• Burned or damaged switch terminals
• Switch remains open when cooled

Installation Tips

1. Disconnect power before servicing equipment.
2. Confirm temperature ratings match the original component.
3. Inspect wiring terminals for corrosion or overheating.
4. Mount securely in the original factory location.
5. Verify proper airflow across the heat exchanger.
6. Test switch continuity during service.
7. Check furnace temperature rise after installation.

Recommended Inspection Items

• Air filter condition
• Blower wheel cleanliness
• Blower motor operation
• Supply and return airflow
• Heat exchanger condition
• Venting system restrictions
• Wiring connections
• Burner operation
• Temperature rise across furnace
• Adjacent safety controls