The 3L09-2 Board Mount Limit Control (White-Rodgers / Copeland Comfort Control) is an automatic reset temperature safety switch designed to protect HVAC equipment, heating systems, and electrical control assemblies from overheating. Featuring a 170°F fixed open temperature and automatic reset operation, this compact board-mounted bimetal limit switch opens the circuit when excessive temperatures are detected and automatically restores operation after cooling, helping protect sensitive components and control circuits from heat damage.

Cross-Reference

• 3L09-2
• 3L092
• L170F
• White-Rodgers 3L09-2
• Copeland Comfort Control 3L09-2
• 74T Series Board Mount Limit Control

Direct OEM

White-Rodgers 3L09-2

Compatible Brands

• White-Rodgers
• Emerson
• Copeland
• York
• Coleman
• Luxaire
• Goodman
• Rheem
• Universal HVAC Applications

Application

Used in HVAC and electrical equipment to:

• Protect control boards from overheating
• Interrupt circuits at elevated temperatures
• Automatically restore operation after cooling
• Safeguard transformers and electrical compartments
• Prevent temperature-related component failure
• Provide automatic overtemperature protection

Related Components

• Board Mount Limit Switch
• Snap Disc Thermostat
• Furnace Control Board
• Transformer
• Blower Relay
• High Limit Control
• Temperature Sensor
• Safety Cutoff Switch
• Electrical Control Assembly

Technician Notes

The 3L09-2 is an automatic reset, open-on-rise board mount limit control utilizing a compact bimetal sensing disc. The switch remains closed during normal operation and opens when the sensing surface reaches 170°F, interrupting the circuit to protect equipment from overheating. Once temperatures fall below the reset threshold, the contacts automatically close and restore operation.

Often used on control boards, electrical compartments, blower assemblies, and OEM equipment where compact temperature protection is required.

Common Symptoms of Failure

• Equipment shuts down unexpectedly
• Open safety circuit fault
• Intermittent operation
• High-temperature shutdowns
• Control board overheating faults
• No continuity through switch contacts
• Failure to reset properly
• Electrical compartment overheating

Installation Tips

1. Disconnect power before servicing.
2. Verify temperature ratings match the original component.
3. Confirm switch action is Open on Rise.
4. Mount securely to the original location.
5. Inspect terminals for heat damage or corrosion.
6. Verify adequate airflow around electrical components.
7. Test continuity after installation.
8. Confirm proper operation during a complete system cycle.

Recommended Inspection Items

• Control board condition
• Transformer temperature
• Wiring harness connections
• Electrical terminals
• Blower motor operation
• Airflow restrictions
• Ventilation around controls
• Relay operation
• Equipment operating temperatures