The 3L09-12 Board Mount Limit Control (White-Rodgers / Copeland Comfort Control) is an automatic reset temperature safety switch designed to protect HVAC equipment, control boards, transformers, and electrical compartments from overheating. Featuring a 220°F fixed open temperature, this compact board-mounted bimetal limit switch interrupts the circuit when excessive temperatures are detected and automatically restores operation after cooling, helping safeguard sensitive electrical components and maintain reliable equipment performance.

Cross-Reference

• 3L09-12
• 3L0912
• L220F
• White-Rodgers 3L09-12
• Copeland Comfort Control 3L09-12
• 74T Series Board Mount Limit Control

Direct OEM

White-Rodgers 3L09-12

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 safety circuits at elevated temperatures
• Automatically restore operation after cooling
• Protect transformers and electrical enclosures
• Prevent temperature-related component failures
• Provide automatic thermal 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 3L09-12 is an automatic reset, open-on-rise board mount limit control utilizing a compact bimetal sensing disc. The contacts remain closed during normal operation and open when the sensing surface reaches 220°F, interrupting the circuit to protect equipment from excessive temperatures. Once temperatures fall below the reset point, the contacts automatically reclose and restore normal operation.

Board-mounted limit controls are commonly used in transformer compartments, control board assemblies, blower sections, electrical cabinets, and OEM HVAC equipment where dependable overtemperature protection is required in a compact footprint.

Common Symptoms of Failure

• Equipment shuts down unexpectedly
• Open safety circuit faults
• Intermittent operation
• Repeated 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 the replacement temperature rating matches 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 airflow around electrical components.
7. Test continuity after installation.
8. Confirm proper operation through a complete equipment cycle.

Recommended Inspection Items

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