The 3L09-9 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 190°F fixed open temperature and 170°F fixed close temperature, this compact board-mounted 1/2-inch bimetal disc limit switch interrupts the circuit when excessive temperatures are detected and automatically restores operation after cooling. Its 3.12-inch insertion length provides reliable temperature sensing for OEM and replacement applications.

Cross-Reference

• 3L09-9
• 3L099
• L190F
• 74T11 Series
• White-Rodgers 3L09-9
• Copeland Comfort Control 3L09-9

Direct OEM

White-Rodgers 3L09-9

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 190°F
• Automatically reclose at 170°F
• Protect transformers and electrical enclosures
• Prevent temperature-related component failures
• Provide automatic thermal protection for HVAC controls

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 3L09-9 is an automatic reset, open-on-rise board mount limit control utilizing a 1/2-inch bimetal sensing disc and 3.12-inch insertion length. The contacts remain closed during normal operation and open when the sensing temperature reaches 190°F, interrupting the circuit to prevent overheating. Once temperatures decrease to approximately 170°F, the contacts automatically reset and restore operation.

This style of limit control is commonly used for protecting control boards, transformer compartments, electrical enclosures, air handlers, and OEM HVAC equipment requiring compact, dependable temperature protection.

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 ratings match the original part.
3. Confirm switch action is Open on Rise.
4. Ensure proper insertion depth during installation.
5. Inspect terminals for heat damage or corrosion.
6. Verify adequate airflow around electrical components.
7. Check continuity after installation.
8. Test 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