The Atwood furnace sail switch is a small yet vital safety device in many RV heating systems. It uses a lightweight paddle, or sail, to sense airflow from the furnace blower and draft inducer. If airflow is insufficient, the switch prevents gas ignition to avoid dangerous buildup. Knowing the sail switch location, how it works, and how to test or replace it helps RV owners troubleshoot heating issues quickly and safely.
Sail Switch Location In Atwood Furnaces
In most Atwood furnaces, the sail switch lives inside the main furnace cabinet, typically near the blower housing or the intake plenum just downstream from the draft inducer. Two small vacuum or tubing lines connect the switch to the air path, and two electrical leads connect to the control board. Exact placement varies by model and year, so consulting the owner’s manual or a service bulletin for the specific unit is advised. A typical sail switch is a compact plastic component with a small paddle that moves with airflow.
- Common placement: behind the burner compartment or beside the blower.
- Connected by two small hoses and a two-wire electrical connector.
- Look for a tiny housing with a movable paddle inside a narrow air passage.
How The Sail Switch Works
The sail switch acts as an airflow sensor that enables gas ignition only when sufficient draft exists. When the furnace blower and inducer start, the paddle deflects with the air stream. If the airflow is adequate, the paddle allows the electrical circuit to close, energizing the gas valve and allowing ignition. If airflow is weak, blocked, or the inducer fails, the switch remains open, cutting gas to the burner and preventing ignition. In essence, it’s a fail-safe to ensure safe combustion.
Key point: The sail switch is typically normally closed and opens with insufficient airflow, stopping gas flow until proper draft is restored.
Identifying A Faulty Sail Switch
Signs of a sail switch problem can mirror other furnace issues. The most common symptoms in Atwood units include a blower that runs without ignition, intermittent ignition failures, or a furnace that starts the blower but shuts down before lighting. A tripping or buzzing sensation from the switch area, accumulated dust, or damaged hoses are visual indicators. If the furnace cannot reach ignition and the blower operates, the sail switch or its connections are prime suspects.
Before diving into diagnostics, ensure the system is safely isolated from gas and power. Do not override safety devices; a faulty sail switch should be diagnosed and repaired to restore safe operation.
Testing The Sail Switch
Testing should proceed with safety as the priority. The process involves electrical checks and a mechanical sense of airflow. If unsure, seek professional service to avoid gas or electrical hazards. The steps below are general guidelines for many Atwood models, but model-specific instructions may differ:
Electrical Continuity Test
Turn off the RV power and, if applicable, shut off the propane supply. Access the sail switch inside the furnace cabinet. Disconnect the two-wire connector from the switch or unplug the leads. Set a multimeter to continuity or ohms. With the paddle in its resting position (no airflow), there should be little to no continuity between the switch terminals. Create airflow by briefly running the inducer or gently moving the paddle with a nonconductive tool; you should see the circuit close (continuity) when airflow is simulated. If there is no change, the switch may be bad or out of adjustment.
Mechanical/Airflow Test
Reconnect the switch harness. Reapply power and, using the thermostat, trigger the furnace to start. Listen for the inducer and blower operation, then observe whether ignition occurs. If ignition still fails but the blower runs, rehearse the airflow path: ensure there are no obstructions in the air intake, cabinet vents, or ductwork. If airflow appears strong yet the switch does not respond, the sail mechanism or mounting may be misaligned or damaged.
Cleaning And Adjustment
Dust, lint, and humidity can affect sail switch performance. A careful cleaning and adjustment can restore proper operation without replacement. Begin by powering down the system and removing the access panel to reach the switch. Use compressed air to gently blow out dust around the paddle and housing. Wipe the exterior with a lint-free cloth. If the paddle is restricted or the air path is blocked, clear the obstruction. Some models include an adjustment screw or a mounting screw to fine-tune paddle travel; follow the manufacturer’s torque specifications when re-securing the switch.
Tip: Ensure the two vacuum hoses are seated properly and free of kinks. A small bend can imitate low airflow and trigger false shutdowns.
Replacement Steps
If cleaning and adjustment do not restore proper function, replacing the sail switch may be necessary. Obtain a replacement part that matches the exact Atwood model year. Replacement steps are generally as follows, but always consult the service manual for model-specific instructions:
- Shut off power and gas, then disconnect the battery or supply to the furnace.
- Open the cabinet and locate the sail switch, noting its mounting orientation and hose connections.
- Carefully unplug the electrical connector and detach the two vacuum hoses from the switch.
- Remove the mounting screws, detach the switch, and compare it to the new unit for fit and lead orientation.
- Install the new sail switch, reattach hoses, reconnect the electrical connector, and secure the switch with the mounting screws.
- Reconnect power, restore gas, and run a test cycle through the thermostat to confirm ignition and airflow operation.
Safety Considerations
Safety is paramount when working on RV heating systems. Always disconnect power before handling electrical components. If gas is involved, ensure the propane supply is turned off when performing maintenance. Work in a well-ventilated area and check for any gas odors after maintenance. If the system shows signs of a persistent failure, such as repeated ignition attempts without flame or abnormal burner behavior, consult a licensed technician to diagnose the issue beyond the sail switch.
Maintenance And Best Practices
- Inspect the sail switch during regular furnace maintenance, typically yearly or per the RV’s service schedule.
- Keep the air intake and vents clean to prevent false readings due to debris.
- Ensure ducting and hoses are free of kinks and blockages that could reduce airflow.
- Document model numbers and part numbers for future replacements to ensure compatibility.
- Do not bypass the sail switch. It is a critical safety component that protects against dangerous gas buildup.
Model Variations And Resources
Atwood has produced multiple furnace models over the years; the sail switch location can vary slightly between vintages. Always refer to the specific model’s service manual, parts catalog, or technician notes for exact diagrams and part numbers. Community forums, RV dealer service centers, and Atwood’s support resources can provide model-specific guidance and troubleshooting tips that reflect the latest design changes.
Summary Of Practical Steps
To locate and assess the Atwood sail switch, identify its position near the blower or intake plenum, inspect the electrical and tubing connections, and verify proper operation through electrical continuity and airflow tests. If cleaning, adjusting, or testing does not restore function, replace the switch with a correct model, then re-test the entire furnace cycle. The sail switch is essential for safe operation, and proper maintenance helps ensure reliable heat in the RV).