Furnace Troubleshooting

[Country Campers]

So I'm a little unclear. Does that mean the sail switch is not accessible unless you remove the unit, then remove the fan housing?

Steve

If you remove the cover on the outside of the RV you will have direct access to the cover that Gene is speaking of. Depending on the year the sail switch actually sticks down a little and I think the newer ones are like the photo that Gene has supplied where the switch is up inside the cover.

Here is what you should see when you remove the outside cover.

[steve&renee]

Thanks to all who chimed in. I did take my rig to the dealer who worked me in between scheduled service appointments. The problem was a loose connection on the igniter board. While waiting for the work to be done, I proactively ordered a Dinosaur replacement board for about $100 from Amazon, and the dealer installed it for me. The dealer asked if I wanted to proactively replace the sail switch while the furnace was out, so I also had them install the $10 sail switch, too.

Total bill from the dealer was a little over $200.

We're going camping next weekend, and depending on COVID, to the high Rockies in late September. And we'll have heat as needed!

-Steve

[RV Tech Ret]

I realize the furnace is working now however I would like to jump in here and correct some misinformation throughout the post.

First off the fan DOES spin if the sail switch is bad....the sail switch is that, a "sail" in the wind, in other words the purpose of the sail switch is to insure the fan is spinning and fast enough. The air moves the sail over and makes contact and then moves the 12VDC onto the thermal switch which if not too hot then send the voltage to the board and says all good. The board then opens the LP valve and starts the igniter.

So in a nutshell, if the fan starts and runs for a short time and the fan shuts off most likely it's the sail switch. You would then need to cycle the thermostat to "reset" the furnace to try it again...the sail switches are known to be "sticky"....

Mark

[howson]

I realize the furnace is working now however I would like to jump in here and correct some misinformation throughout the post.

First off the fan DOES spin if the sail switch is bad....the sail switch is that, a "sail" in the wind, in other words the purpose of the sail switch is to insure the fan is spinning and fast enough. The air moves the sail over and makes contact and then moves the 12VDC onto the thermal switch which if not too hot then send the voltage to the board and says all good. The board then opens the LP valve and starts the igniter.

So in a nutshell, if the fan starts and runs for a short time and the fan shuts off most likely it's the sail switch. You would then need to cycle the thermostat to "reset" the furnace to try it again...the sail switches are known to be "sticky"....

Mark

Mark,
Are you stating the board does not verify the sail switch is open before applying power to the fan, as documented in the Suburban manual?

In other words, the way I interpret what the manual is stating is if the sail switch is stuck closed power will never be applied to the circuit to turn on the fan.

Is that wrong?

Howard

[RV Tech Ret]

Mark,
Are you stating the board does not verify the sail switch is open before applying power to the fan, as documented in the Suburban manual?

In other words, the way I interpret what the manual is stating is if the sail switch is stuck closed power will never be applied to the circuit to turn on the fan.

Is that wrong?

Howard

I understand what your saying:

From the manual: Upon a call from the thermostat, the module board thermostat circuit will go active. The sail switch circuit is verified as being open. The blower output is energized. Blower motor starts.

What I will tell you is the "natural" position of the sail switch is open - in all my years I have never seen a sail switch "stuck" closed. The failure mode is it will not "sail" to the closed position after the fan has started.....

Mark

[howson]

I understand what your saying:

From the manual: Upon a call from the thermostat, the module board thermostat circuit will go active. The sail switch circuit is verified as being open. The blower output is energized. Blower motor starts.

What I will tell you is the "natural" position of the sail switch is open - in all my years I have never seen a sail switch "stuck" closed. The failure mode is it will not "sail" to the closed position after the fan has started.....

Mark

Thanks, Mark. I have zero personal experience troubleshooting a furnace (though I understand the concepts and process if I need to do it). I appreciate the clarification and insight.

Howard