The 3L09-19 Board Mount Limit Control (White-Rodgers / Copeland Comfort Control) is an automatic reset temperature safety switch designed to protect HVAC equipment, control boards, transformers, electric heating systems, and electrical compartments from overheating. Featuring a 175°F fixed open temperature and an extended 7.5-inch insertion length, this compact board-mounted bimetal limit switch interrupts the circuit when excessive temperatures are detected and automatically restores operation after cooling, providing dependable thermal protection for critical system components.

Cross-Reference

• 3L09-19
• 3L0919
• L175F
• White-Rodgers 3L09-19
• Copeland Comfort Control 3L09-19
• 74T Series Board Mount Limit Control

Direct OEM

White-Rodgers 3L09-19

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 enclosures
• Safeguard electric heat assemblies
• Prevent temperature-related component failures

Related Components

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

Technician Notes

The 3L09-19 is an automatic reset, open-on-rise board mount limit control utilizing a compact bimetal sensing disc with a 7.5-inch insertion probe for applications requiring deeper temperature sensing. Under normal operating conditions, the contacts remain closed and open when the sensing surface reaches 175°F, interrupting the circuit to prevent overheating. Once temperatures fall below the reset threshold, the contacts automatically reclose and restore operation.

The extended probe design is commonly used in air handlers, electric heat packages, control compartments, and OEM HVAC equipment where standard insertion lengths are insufficient to accurately monitor component temperatures.

Common Symptoms of Failure

• Equipment shuts down unexpectedly
• Open safety circuit faults
• Intermittent operation
• Repeated thermal shutdowns
• Electric heat lockouts
• 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 control.
3. Confirm switch action is Open on Rise.
4. Verify the 7.5-inch insertion length matches the application.
5. Secure the sensing probe properly during installation.
6. Inspect terminals for corrosion or heat damage.
7. Test switch continuity after installation.
8. Verify operation through a complete heating cycle.

Recommended Inspection Items

• Control board condition
• Transformer temperature
• Wiring harness connections
• Electrical terminals
• Blower motor operation
• Airflow restrictions
• Electric heat elements
• Relay condition
• Ventilation around controls
• Probe insertion depth