Furnace 350 Rollout Limit Switch Instruction Manual

1. Product Overview

The LLPParts Furnace 350 Rollout Limit Switch (Part Number B13701-54) is a critical safety component designed for use in various furnace models. This manual reset switch is engineered to detect excessive temperatures, typically caused by flame rollout, and interrupt the furnace's operation to prevent potential hazards.

It is rated for a maximum temperature of 350 degrees Fahrenheit (176.6 degrees Celsius) and features a manual reset mechanism, meaning it must be physically reset after it has tripped due to an over-temperature condition.

Image: The LLPParts Furnace 350 Rollout Limit Switch, showing its manual reset button (red) and two electrical terminals.

This switch is compatible with a wide range of furnaces, including but not limited to models such as GMP050-3, GMP075-3, GMP100-4, GMP125-5, GMP150-5, GMPE075-3, GMPE100-4, GMPE125-5, GMPH050-3, GMPH075-4, GMPH080-5, GMPH120-5, GPD050-3, GPD075-3, GPD100-4, GPD125-4, GMPN040-3, GMPN060-3, GMPN080-4, GMPN100-4, GMPN120-5, GSMS060-3, GSMS080-4, GSMS100-4, GSM060-3, GSM080-4, GSM100-4, and various PGB and PGJ series furnaces. Refer to your furnace's specific documentation for exact compatibility.

2. Setup and Installation

Important Safety Information: Installation of this component involves working with electrical systems and gas appliances. It is highly recommended that installation be performed by a qualified HVAC technician. Failure to follow proper safety procedures can result in property damage, serious injury, or death.

1. Disconnect Power: Before beginning any work, ensure that all electrical power and gas supply to the furnace are completely disconnected at the main breaker and gas shut-off valve. Verify power is off using a voltage tester.
2. Locate Existing Switch: Identify the location of the existing rollout limit switch on your furnace. It is typically mounted near the burner assembly or heat exchanger.
3. Remove Old Switch: Carefully disconnect the electrical wires from the old switch. Note the orientation of the wires if they are not interchangeable. Remove any mounting screws or clips securing the old switch.
4. Install New Switch: Position the new LLPParts Rollout Limit Switch in the same location as the old one. Secure it using the appropriate mounting hardware.
5. Connect Wiring: Reconnect the electrical wires to the terminals on the new switch. Ensure connections are secure and free from corrosion.
6. Restore Power: Once the switch is securely installed and wired, restore the gas supply and electrical power to the furnace.
7. Test Operation: After installation, carefully test the furnace operation to ensure it functions correctly. Observe for any unusual behavior.

Always consult your furnace's specific service manual for detailed installation instructions and wiring diagrams.

3. Operating Principles

The rollout limit switch is a normally closed safety device. Its purpose is to monitor the temperature in the burner compartment or heat exchanger area. If the temperature exceeds its calibrated limit (350°F), typically due to flame rollout or a blocked heat exchanger, the internal bimetallic disc in the switch will open, breaking the electrical circuit to the furnace's gas valve or control board. This action immediately shuts down the furnace to prevent overheating and potential fire hazards.

Because it is a manual reset switch, once it trips, it will remain open until it is physically reset by pressing the small red button located on the switch. This manual reset feature is a safety measure, requiring a technician or homeowner to investigate and resolve the underlying cause of the over-temperature condition before the furnace can be restarted.

4. Maintenance

The LLPParts Rollout Limit Switch is a robust component designed for long-term reliability. Regular maintenance of your furnace system is crucial for its proper function and longevity. While the switch itself requires minimal direct maintenance, consider the following:

• Annual Inspection: During routine furnace maintenance, have a qualified technician inspect the rollout limit switch for any signs of physical damage, corrosion on terminals, or loose wiring.
• Cleanliness: Ensure the area around the switch is free from dust, debris, or obstructions that could interfere with its temperature sensing capabilities.
• Do Not Bypass: Never attempt to bypass or disable the rollout limit switch. It is a critical safety device designed to protect against dangerous conditions. Bypassing it can lead to severe safety risks.

5. Troubleshooting

If your furnace is not operating and you suspect the rollout limit switch has tripped, follow these troubleshooting steps:

Symptom: Furnace does not ignite or operate, and the rollout limit switch is tripped (red button popped out).

Possible Causes:

• Flame Rollout: Flames escaping the combustion chamber, often due to a cracked heat exchanger, blocked flue, or improper gas pressure.
• Blocked Flue/Vent: Obstructions in the furnace's exhaust system preventing proper venting of combustion gases.
• Dirty Burners: Clogged or dirty burners can cause incomplete combustion and flame irregularities.
• Insufficient Combustion Air: Lack of adequate fresh air for combustion.
• Heat Exchanger Issues: Cracks or blockages within the heat exchanger can lead to localized overheating.

Resolution Steps:

1. Safety First: Immediately disconnect power and gas to the furnace.
2. Identify and Rectify Cause: The most crucial step is to determine and correct the underlying reason for the switch tripping. This often requires a qualified HVAC technician to diagnose the furnace system thoroughly. Do not simply reset the switch without addressing the cause, as this can be dangerous.
3. Allow Cooling: Let the furnace cool down completely for at least 15-30 minutes.
4. Manual Reset: Once the furnace has cooled and the cause has been addressed, locate the small red button on the rollout limit switch and firmly press it until it clicks into place.
5. Restore Power and Test: Restore power and gas to the furnace. Attempt to restart the furnace.

If the switch trips repeatedly, or if you are unable to identify and resolve the cause, contact a certified HVAC professional immediately. Repeated tripping indicates a serious safety issue with your furnace.

6. Specifications

7. Warranty and Support

Warranty Information: This LLPParts product comes with a one-year warranty from the date of purchase. This warranty covers defects in materials and workmanship under normal use. Please retain your proof of purchase for warranty claims.

Customer Support: For technical assistance, troubleshooting beyond the scope of this manual, or warranty inquiries, please contact the seller or manufacturer directly through the platform where the product was purchased. Provide your product model number (74) and part number (B13701-54) when seeking support.