Airxcel Furnace Not Working When Thermostat Switched to Heat

Tools & Parts Needed

Find these on Amazon: Digital Multimeter , RV Thermostat , Wire Stripper Set

Quick Answer

When your Airxcel furnace doesn't respond to thermostat commands, common causes include power supply issues, faulty thermostat wiring, or a problem with the furnace control board. The good news is that most of these issues can be diagnosed and often fixed without calling a technician.

What You'll Need

• Digital multimeter
• Wire strippers and electrical tape
• Screwdrivers (Phillips and flathead)
• Flashlight or headlamp
• Wire nuts or crimp connectors
• 12V test light (optional but helpful)

Step-by-Step Troubleshooting Guide

1. Check the obvious first: Verify your propane tanks are open and have fuel. Even though this seems basic, I've seen countless RVers overlook this simple step. Also ensure your battery disconnect switch is on and batteries are charged above 12.2 volts.
2. Test thermostat power: WARNING: Turn off power at the main breaker before working with electrical connections. Remove your thermostat from the wall (most pop off or have two screws). Using your multimeter, check for 12V DC between the red (power) and white (common) wires. No voltage here means the problem is upstream in your electrical system.
3. Verify thermostat operation: With the thermostat removed, use insulated wire nuts to connect the red wire to the yellow wire (heat call signal), then restore power while monitoring the furnace. If it fires up, your thermostat is bad and needs replacement.
4. Check furnace power supply: Locate your Airxcel furnace (usually in a basement compartment or interior access panel). Find the wire harness connection and verify 12V power is reaching the furnace control board on the red wire.
5. Inspect wiring connections: Look for loose, corroded, or damaged connections at both the thermostat and furnace ends. Airxcel furnaces are particularly sensitive to voltage drop, so even slightly loose connections can prevent operation.
6. Test the sail switch: Inside the furnace, locate the small sail switch (a thin metal flap). Gently push it closed while calling for heat - if the furnace attempts to start, the blower motor may be weak or the switch may need adjustment.
7. Examine the control board: Look for any obvious signs of damage like burnt components, loose connections, or corrosion. Many Airxcel control board failures are visible to the naked eye.

Common Causes and Solutions

Weak batteries or poor charging: Airxcel furnaces need solid 12V power to operate reliably. If your battery voltage drops below manufacturer specifications under load (verify with dealer documentation), the furnace may not start even though other systems seem fine. Test your batteries under load and ensure your converter is working properly.

Thermostat wiring issues: The most common problem I see is reversed or loose thermostat wires. Airxcel systems use a standard color code: red (12V+), white (common), yellow (heat), and sometimes green (fan). Double-check these connections match your thermostat manual.

Control board failures: Airxcel control boards can fail due to power surges, moisture, or age. If you've verified power and proper thermostat signals but still no response, the board likely needs replacement. These typically cost $150-250 (prices may vary by location and supplier).

Blocked or restricted airflow: A dirty filter or blocked return air can prevent the sail switch from operating properly. Always check your air filter first - it should be cleaned or replaced monthly during heavy use.

Advanced Troubleshooting

Testing the High Limit Switch

WARNING: Ensure furnace is completely cool and power is disconnected before testing electrical components. If your furnace starts but shuts down quickly, the high limit switch may be tripping due to restricted airflow or a bad heat exchanger. This switch can be tested with a multimeter for continuity when cool.

Propane Pressure Issues

While less common, low propane pressure can cause starting problems. If your stove or water heater also run poorly, have your propane system pressure tested by a qualified technician.

When to Call a Professional

Call a professional immediately if: You smell gas around the furnace, see any signs of carbon buildup or soot, or if the furnace makes unusual noises during operation. Also, if you're not comfortable working with 12V electrical systems or propane appliances, don't hesitate to get help.

Additionally, if you've gone through these troubleshooting steps and still can't identify the problem, a qualified RV technician can perform more advanced diagnostics like checking gas valve operation and heat exchanger integrity.

Prevention and Maintenance Tips

Regular maintenance prevents most Airxcel furnace problems. Clean or replace air filters monthly, keep exterior vents clear of debris, and have your propane system inspected annually. Also, run your furnace briefly each month during storage to keep components exercised.

Consider carrying a spare thermostat and basic electrical supplies in your RV toolkit. Thermostats are relatively inexpensive and fail more often than other components, especially in older RVs with temperature cycling issues.

Finally, keep your battery system in top condition. More RV furnace problems stem from electrical issues than propane problems, and a well-maintained 12V system prevents most of these failures. Regular battery maintenance and proper charging system operation are essential for reliable furnace operation throughout your RV adventures.