Quickly Testing Gas Furnace Safety/Limit Switches!

Summary

In this informative video, Craig Migliaccio from AEC Service Tech guides viewers through troubleshooting safety sensors in gas furnaces. He demonstrates how to test flame rollout switches, thermal limit switches, and pressure switches using a multimeter, emphasizing the importance of safety in furnace operation. The video explains the functionality of various components, including the flame sensor, and offers tips for maintenance. Viewers are encouraged to explore additional resources and quizzes available on the AEC Service Tech website to enhance their knowledge of gas furnace systems.

Takeaways

• 😀 Familiarize yourself with key components like flame rollout switches, thermal limit switches, pressure switches, and flame sensors in gas furnaces.
• 🔧 Use a multimeter to test components by measuring resistance across contacts to determine if they are open or closed.
• ⚡ When measuring voltage, connect one probe to ground and the other to the component to check for consistent voltage readings.
• 📊 A closed flame rollout switch will show close to 0.0 ohms of resistance and consistent voltage across its contacts, confirming it's functioning properly.
• 🔒 Safety sensors are powered at all times when the furnace is on, helping to detect flame issues even when not in heating mode.
• 💡 If there's a crack in the heat exchanger, flame rollout switches will trip, indicating a serious safety concern and potential carbon monoxide exposure.
• 📈 Test the pressure switch while the furnace is in heating mode; a reading of around 28 volts indicates that it is closed and functioning correctly.
• 🔥 The flame sensor continuously checks for flame presence; do not touch it while the furnace is powered on for safety reasons.
• 🧼 Regular maintenance of the flame sensor includes cleaning it with non-soap steel wool or a dollar bill to ensure proper operation.
• 📚 Explore AEC Service Tech's website for free resources, quizzes, and educational materials on gas furnace maintenance and troubleshooting.

Q & A

What is the purpose of the flame rollout switch in a gas furnace?

The flame rollout switch is a safety device that prevents flames from escaping the furnace if there is a crack in the heat exchanger, helping to avoid potential carbon monoxide hazards.

How do you test a flame rollout switch using a multimeter?

To test a flame rollout switch, disconnect the wires and measure the resistance across the contacts with a multimeter. A reading of 0.0 ohms indicates that the switch is closed.

What does it mean if you read no voltage drop across a safety switch?

If there is no voltage drop across a safety switch, it means that the contacts inside the switch are closed and functioning correctly.

What should you do if the thermal limit switch opens?

If the thermal limit switch opens, it indicates that the temperature is too high, likely due to issues like a malfunctioning blower motor or an overfiring furnace.

How does the pressure switch function in a gas furnace?

The pressure switch ensures that the inducer motor is working correctly by checking that it is pulling the right pressure. It only has power across it when the control board is sending power to the inducer motor.

What voltage reading is normal for a flame sensor in a gas furnace?

The flame sensor typically reads around 108 volts when power is applied, as it continuously checks for the presence of a flame.

What maintenance is recommended for the flame rod in a gas furnace?

The flame rod can be cleaned with non-soap steel wool or a dollar bill. It should only be replaced if it is significantly corroded, melted, or bent.

Why is it important to test safety sensors even when the furnace is not in heating mode?

Testing safety sensors is crucial because they continuously monitor for unsafe conditions, such as flame presence, even when the furnace is off or in air conditioning mode.

What resources does AEC Service Tech offer for further learning?

AEC Service Tech offers free articles, quick tips, quizzes, calculators, a book on air conditioning, and a thousand-question workbook for self-study.

What precautions should be taken when testing the flame rod?

When testing the flame rod, ensure that the power to the furnace is turned off to prevent electric shock or damage to the equipment.