Ultimate Guide On Understanding Why Your RV Furnace Is Blowing Cold Air

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When it’s cold outside, an RV furnace problem is your top priority.

It is helpful to understand the primary function of your RV furnace to help diagnose the problem. Any RV furnace (regardless of a Suburban Furnace or an Atwood Furnace) all part on the same basic principles. There is an electrical connection (12V for the blower), a fuel source (usually propane), and heat provided through combustion (through a heat exchanger). Even an older furnace will operate under this basic principle.

If you have an electric heater, the fuel source will be electricity. Many of the checklist items still apply, such as fuses and thermostat settings.

Table of Contents

Electrical Connection

The primary electrical function of your heater is to run the blower motor. If your gas furnace is blowing cold air, it is a sign that there is an electrical connection. However, your heater may want a particular amount of volts (above 12V) to operate correctly and trigger the other heater functions.

Even when your AC power is converted to the needed 12V DC on shore power. You might be getting some airflow, but the total capacity without the proper voltage. Check your battery voltage and confirm you have 12V to 14V. Anything lower may not operate the furnace blower. For info on batteries and how your RV uses them, visit my post on RV Batteries.

Fuel Source

Your RV heater is likely powered by propane. This propane is a combustible fuel that serves as the heat for your furnace that provides the warm air. Propane is usually located at the front of your RV and has a series of hoses or pipes that supply things like your stove, hot water tank, and furnace.

Heat Exchanger

RV furnaces work by using a heat exchanger to transfer heat from the propane flame to the air passing over the exchanger. The air is then blown through the RV and warms up. The furnace will continue to run until the temperature in the RV reaches the thermostat setting.

Why Is My RV Furnace Blowing Cold Air?

Now that you know the basic set-up of an RV furnace go through the following troubleshooting procedure and see why there is cold air.

Gas Supply

I always like to start with the simplest and the most common reasons something may not be working. If your heater is blowing cold air, the good news is that it is getting power (the blower motor) and that the issue is likely a fuel source (propane) since it is not generating heat. Even a seasoned RVgoer (such as myself) has been known to forget to turn on the propane tank and assume something was wrong.

After you check that the propane tank gas valve is on and you are still getting cold air, check that you have propane in the tank. There are some gauges and tips you can do to get a sense of how much propane is in your tank. Those are fine and dandy, but I prefer to link up the tank and swish it around to see if there is any liquid propane in there. Sometimes that little bit of movement gets the fuel going.

Check Fuse

Although it is unlikely a fuse, I would still check the heater fuse for any issues since you have your power. The fuse is located in the electrical panel, and it’s usually a small, round, red fuse. If the fuse is blown, replace it with a new one of the same size and rating. If the furnace still doesn’t work, keep following the steps below.

Thermostat Setting

If your RV heater is not working, the first thing you should check is the thermostat. People often assume that the heater is broken when it’s just turned off. Ensure that the thermostat is in the on position and set to the desired temperature. Sounds silly, but if it’s 60 degrees in your RV and the thermostat is set at 55, your furnace will not provide hot air.

Also, if you have a fireplace, you may have a switch (see photo below) that may be in the wrong position. This switch acts as a cur off switch so you don’t accidentally run your air conditioner while running your fireplace (that would waste a ton of energy). Check this switch is set to Furnace and that it also seems to be in proper working order (these switches can go bad, but not as likely).

Check Sail Switch

The sail switch is a small, triangular piece of metal that hangs down from the blower housing and contacts the burner assembly. If it’s not making contact, the furnace won’t light. Remove the access panel on the furnace and look for the sail switch to check it. Gently move it up and down with your fingers to see if it’s moving freely. If it’s not, you’ll need to clean or replace it.

Replacing the sail switch is a relatively straightforward process. The first step is to remove the blower assembly from the furnace. This can be done by removing the screws that hold it in place. Once the blower assembly is removed, the sail switch can be accessed and replaced. Reinstalling the blower assembly is just as easy as removing it. Replace the screws and reattach the wiring harnesses. Once everything is back in place, test your RV furnace to make sure it’s working correctly.

Check Flame Sensor

The sensor is located on the burner assembly and looks like a small metal rod. If it’s dirty or covered in soot, it won’t be able to sense the flame, and the furnace will shut down. You can clean it with a wire brush or a vacuum cleaner. If that doesn’t work, the sensor may be defective and need to be replaced.

Check The Exhaust Is Not Blocked

It is not uncommon for rodents to build a nest in your exhaust. Without the ability of your heater to remove all of that heat, the furnace can be overheating. This will cause the furnace burner to shut down and not ignite.

To check your blower, get a flashlight and look inside. If you see anything, get a shop vac or compressed air to remove anything that will allow the warm air to escape. When the RV furnace is working properly, the exhaust air will be very hot and not cold or cool air.

Conclusion

If your RV furnace is not working, there are a few potential causes that you can troubleshoot. One of the most common problems is a lack of propane. Be sure to check the gauge on your propane tank to ensure you have enough fuel. If the furnace still will not ignite, it may be due to a faulty thermostat or sail switch. Try replacing these parts to see if that solves the issue.