The 3L09-3 Board Mount Limit Control (White-Rodgers / Copeland Comfort Control) is an automatic reset temperature safety switch designed to protect HVAC equipment, heating systems, control boards, and electrical assemblies from overheating. This compact board-mounted bimetal limit switch opens the circuit when unsafe temperatures are reached and automatically resets after cooling, helping safeguard sensitive electrical components and ensure reliable equipment operation.

Cross-Reference

• 3L09-3
• 3L093
• White-Rodgers 3L09-3
• Copeland Comfort Control 3L09-3
• 74T Series Board Mount Limit Control

Direct OEM

White-Rodgers 3L09-3

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
• Open safety circuits at elevated temperatures
• Automatically restore operation after cooling
• Protect transformers and electrical compartments
• Prevent temperature-related component failures
• 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 3L09-3 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 its rated temperature is reached, interrupting the circuit to protect equipment from overheating. Once the temperature falls below the reset point, the contacts automatically close and restore operation.

Board-mounted limit controls are commonly used for protecting control boards, transformers, blower compartments, electrical enclosures, and other heat-sensitive HVAC components.

Common Symptoms of Failure

• Equipment shuts down unexpectedly
• Open safety circuit fault
• Intermittent operation
• Repeated high-temperature trips
• 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 in the original location.
5. Inspect terminals for corrosion or heat damage.
6. Verify adequate ventilation around electrical components.
7. Test continuity after installation.
8. Confirm proper system operation after replacement.

Recommended Inspection Items

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