I’ve been struggling with my RV furnace blowing cold air the past few days, but I haven’t had any need to troubleshoot, knowing that the arctic chill is to blame. But there are several other reasons for an RV furnace to blow cold air.
Andy Baird left some great troubleshooting info in a comment to a previous post and I wanted to make sure that readers who don’t look at comments get it. Thanks for this, Andy!
“One common reason for the furnace blowing cold air is low battery voltage.
Unlike a residential furnace, in which the blower doesn’t start until the plenum has warmed up, an RV furnace starts blowing immediately. That’s because it uses the same motor to power both the hot-air blower and a second, isolated blower that moves air through the combustion section.
If the batteries were too weak to power the blowers, or if the motor failed while the burner was lit, the furnace would quickly become a fire hazard. So as a safety feature, there’s an air-sensitive switch in the duct that has veto power over the burner’s gas valve. If this “sail switch” is not activated by sufficient airflow, the burner will not light, or if already lit, will shut off.
That situation can occur when the house batteries are weak. The blower motor spins, but not fast enough to deflect the sail switch. The result: a furnace that blows cold air. It happened to me the first time I camped in wintertime.
It’s also possible for the sail switch to get stuck, due to dust, rust, or insect nests. If you have propane and your battery situation looks good, this is a possibility.
Finally, some possible problems with the propane system include valves, hoses or regulator frozen due to moisture in the system, extreme low temperatures (propane liquifies at -42° C., so if it’s colder than that, it will never vaporize and you won’t have gas pressure), and too much butane in the propane.
Propane is typically sold mixed with butane, and in warm weather this is no problem. But butane liquifies at -1° C, so at any temperature below freezing butane won’t vaporize. Now, your local dealer’s supplier should have made seasonal adjustments to their mix… but if they have a load of propane left over from summer, it may contain so much butane that it won’t vaporize adequately in cold weather. There’s not much you can do about this except switch dealers (if there’s another one nearby) or hope that your local dealer runs through his supply of the less-volatile mix.”
Propane may not vaporize at all at -41 but even at -20 it’s ability to vaporize slows down. With the furnace putting a constant draw on the tank the pressure may get low enough that the furnace fails to fire. When the furnace stops drawing Propane the pressure will rebuild. The solution maybe to go to a bigger tank or to hook more tanks together to maximize the ability of the propane to vaporize. Have you checked with the propane company about renting or acquiring a Larger tank? In Alberta we would call them a pig but there are tanks that are about 500 lbs. The propane company would have to come out to refill it but it would have the ability to vaporize more Propane. the other option would be 100 lb tanks.
Don
Thanks Rae! This is extremely valuable information. I have had this problem on occasion but never understood what the problem was. I start camping early in spring and continue into late fall. It isn’t intuitive to think your battery might be too low if there is enough juice for the fan to blow air.
My furnace is diesel fueled so this may not apply to yours but if I get too much carbon buildup in it my furnace will blow cold. The tech realigned my outlets so the output is not blowing so close to the input to reduce this happening–so far so good.
My rv furnace blows hot air till the temperature is met on the thermostat. Then the heat shuts down but the fan keeps blowing cold air.
Hi Marcie. Is this a new problem after your furnace has worked fine for a while or is this your first time dealing with this furnace and it’s always behaved that way? What kind do you have? How old is your RV? Does the furnace run on propane?
Hi did you ever figure out why you’re furnace was blowing cold air?
My RV furnace does this and will not relight on its own, I have to turn the thermostat on and off multiple times to get it to light again. Please let me know how you solved the problem.
Thanks
Rob
Hi Rob,
In my case it was REALLY cold out and my propane was freezing! While not an ideal situation, I had to keep the spare tank inside the RV and rotate it with the outside tank.
My 2018 travel trailer is blowing cold air. Every time the furnace kicks on it blows cold air about 20secs then shuts down. Power is hooked to house and programs tank is brand new just filled. Checked all breakers and no blockage on outside of furnace. Help
Hi Katherine,
What I would try is shutting everything off and closing the propane valve. Wait a few seconds and then open the propane valve very slowly until you hear a hiss. Then open all the way slowly. There is an emergency shutoff on the valves that can activate if they are opened too quickly. Hope that helps!
Hi we have a 2008 Salem Edge 26 foot travel trailer.Everything is working on the trailer except the furnace is blowing cold air,It was working all along until my husband took off the two propane tanks to get the two of them filled up.One of the tanks were expired and that is the reason why we took off the two tanks the same time.We filled up the good tank and we replaced the expired one with a new propane tank. He is after trying everything but the furnace won;t blow warm air.What advoice do you have to fix this problem.We baught the trailer 2 nd hand and we don’t have any book on the trailer.Thank You.
I replied to this comment by email, but thought I’d share here as well.
I am in no way an RV expert, but if everything else seems to be working fine as per this post, then you might have a problem I had when I was switching my external tank with regard to the flow-limiting valve.
Have a look at this post: http://www.raecrothers.ca/blog/propane-is-no-fun-at-all/
It took me quite a while to master hooking up and opening the propane tank valve in a way that would not trigger the flow-limiting valve.
I hope this helps!
Its around 30°. Yet earlier furnace blew hot air, now went cold. Have propane… Best suggestion on fix? Totally lost on this one…
If you’ve tried the suggestions in this post, you might have a case of the safety valve on your tank acting up, especially if you just changed the tank. Check out this post: http://www.raecrothers.ca/blog/propane-is-no-fun-at-all/
Our oven is working so there is propane coming through yet the heater blows cold air then shuts off. The pilot is lit. Now I don’t know what to do.
I have a 2019 Entgra Reatta with 2 gas furnaces. One operates perfect, the 2d one shuts down after blowing cold air.
I have a 2019 Coleman Lantern, we have had it since May 2019. We have only used it about 5 times. We used the furnace in November 2019 seemed to work perfect. We used it again in March 2020 and only got cold air. Everything else that ran off gas worked fine.(water heater and stove) We have a lot lined up to finally use our Travel Trailer I do not want to have to sit it at the dealership for something if I can figure it out, please help??
Hi happy RV’ers! I’m a first-timer, not just posting on an RV site, but also owning & living in a travel trailer camper, it ain’t fancy but it’s great & it’s given me a new form of freedom & is a lot better than being in the abusive relationship I was in oh, and it’s MINE!! 😃
And I do live in it full-time at an RV Park near Lake Lavon in Texas. Anyway, one of the main issues I’ve been having on & off for over a week is that the furnace will come on while the AC is on & running, the AC is blowing cold air from ceiling vents & furnace is blowing hot air from floor vents, it’s done that 2-3 times but today the AC is on off on thermostat & furnace came on & was blowing cool air from vents this time?? And what makes it more of a mystery is that even though I cut the wire for heat at thermostat there was still very warm air blowing & the floor was burning up too?! I also even tried pulling furnace fuse in fuse box, but when I did that, AC wouldn’t come on at all etc!!?? Oh I also bought a new ($100.00) thermostat too thinking that may be the issue but it was not 😐 . I can’t keep the furnace unplugged cause anyone that knows Texas & it’s weather knows it start getting pretty warm this time of year, not to mention that I also have my 102lb. German Shepherd “Fur-baby” too & it’ll get way too hot in there for him!! I’ve read several different things online about issue but don’t quite understand what they’re talking about? Can I fix it myself or do I need pay out the wha-zoo for someone to come out? Ugh!! Any suggestions, ideas? Thanks y’all!!
Jodi 🐾
Sorry, this is Jodi again, forgot to tell you about my trailer:
1998 22ft. Mallard by Fleetwood (Model- 26M)
Thanks again!