Furnace kicks on, blows cool air briefly then turns off

[SouthernCamper]

First, I apologize if this has been discussed. I'm on mobile and search isn't working.

We're on the road and our furnace isn't working. It will turn on briefly, blow cool air for around 30 seconds then turn off. Initially we thought it was a battery issue because our batteries have been acting up (see below in case you have any input there!) but it also won't work in shore power.

We're heading above 10,000 feet tonight and would appreciate any ideas on how to get warm!

---bonus battery issues---while on solar, our batteries will charge to 90%. Power drains quickly from the batteries, leading to blinking overhead lights when using the water pump, inability to open the awning, etc. A few hours after showing full, the monitor lights above the fridge will show that the batteries are empty and the above issues are present. However, the actual charge screen in the bench will sometimes show 60-70% despite the lights reading empty. I'm tempted to say that the lights are just wrong, but the low monitor lights do coincide with evident low power. Do we need new batteries?

[davidmurphy02]

Your furnace issue sounds like a sail switch problem if it quits after the blower runs 30 seconds. Try it again and leave it on at the thermostat after it fails. Then go remove the cover on the outside panel, there should be an LED flashing on the circuit board. There's a sticker mounted on the blower motor housing below that will tell you what 1,2,or 3 flashes mean. If it is the sail switch (indicated by an air flow error code), you can often remove it and clean/blow off the contacts, reinstall it, and it will work again, at least for a while. In my experience once a switch fails it will fail again so ultimately good to just replace it.

In the photo the screwdriver is pointing at the sail switch - there is one screw to remove from the black mounting block, pull the two wires off, and then wiggle it out.

[Chris R]

Originally Posted by SouthernCamper

---bonus battery issues---while on solar, our batteries will charge to 90%. Power drains quickly from the batteries, leading to blinking overhead lights when using the water pump, inability to open the awning, etc. A few hours after showing full, the monitor lights above the fridge will show that the batteries are empty and the above issues are present. However, the actual charge screen in the bench will sometimes show 60-70% despite the lights reading empty. I'm tempted to say that the lights are just wrong, but the low monitor lights do coincide with evident low power. Do we need new batteries?

Have you checked the battery fluid levels?

[SouthernCamper]

Originally Posted by Chris R

Have you checked the battery fluid levels?

Yes we have. Before leaving, we added distilled water. The tops of some of the metal parts (sorry forgot the name!) were just barely exposed. I learned later that I was supposed to fill to just cover them, let a charge cycle run then fully charge but I didn't do this as I wasn't aware at the time.

[SouthernCamper]

Originally Posted by davidmurphy02

Your furnace issue sounds like a sail switch problem if it quits after the blower runs 30 seconds. Try it again and leave it on at the thermostat after it fails. Then go remove the cover on the outside panel, there should be an LED flashing on the circuit board. There's a sticker mounted on the blower motor housing below that will tell you what 1,2,or 3 flashes mean. If it is the sail switch (indicated by an air flow error code), you can often remove it and clean/blow off the contacts, reinstall it, and it will work again, at least for a while. In my experience once a switch fails it will fail again so ultimately good to just replace it.

In the photo the screwdriver is pointing at the sail switch - there is one screw to remove from the black mounting block, pull the two wires off, and then wiggle it out.

Thank you so much for the details and the photo! We will do this as soon as we arrive, and hopefully it will keep the family warm tonight!!

[rog mich]

Originally Posted by davidmurphy02

Your furnace issue sounds like a sail switch problem if it quits after the blower runs 30 seconds. Try it again and leave it on at the thermostat after it fails. Then go remove the cover on the outside panel, there should be an LED flashing on the circuit board. There's a sticker mounted on the blower motor housing below that will tell you what 1,2,or 3 flashes mean. If it is the sail switch (indicated by an air flow error code), you can often remove it and clean/blow off the contacts, reinstall it, and it will work again, at least for a while. In my experience once a switch fails it will fail again so ultimately good to just replace it.

In the photo the screwdriver is pointing at the sail switch - there is one screw to remove from the black mounting block, pull the two wires off, and then wiggle it out.

Thank you David. We were having this exact problem. I clean out the sail switch (thanks for the photo!) and now the heater works!!

[paulw]

Sounds like bad sail switch, BUT, I had the same thing happen dry camping when my batteries were old. I was able to get the heater going by hooking up to my truck to heat the trailer before bed. I don't remember what the voltage was, but it seems there wasn't enough to run the fan fast enough to open close the sail switch.
New batteries fixed it...