Day: December 7, 2013

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Troubleshooting an RV Furnace Blowing Cold Air

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.”

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Arctic Front

The last few days have been… trying. We are experienced incredibly unusual colds do to an Arctic air mass. This cold is being experienced all the way down the Plains, from Omaha to Dallas and beyond.

The first bitter night was that of Wednesday to Thursday and I sailed through it. Thursday, I accepted that keeping the temperature in here above 60F wasn’t reasonable, so I added a shawl and kept working.

I had done some tests earlier in the week and found that I wouldn’t be able to get internet at Laura’s unless I put a pole on the roof, and even then there was no guarantee. Since this cold was supposed to last only a few days, it made more sense to stand my ground at home.

I slept soundly through the night of Thursday to Friday and awoke to find my loft curtains very stiff. It was bitterly cold in the rig, 40F. The furnace was blowing cold air. I went outside to switch tanks and noticed that my 30lber felt way too heavy to be empty. Hmm.

Once I managed to get the furnace going again with another tank, I considered abandoning ship. I knew that it would likely take all day to get the temperature back up again. My biggest fear about the deep freeze had just happened, the temperature inside had plummeted and I had to bring it back up. But 40F or not, I had internet work to do, so I added a couple of layers and got to to work, frustrated that I needed to go to town for propane when I hadn’t planned that in my schedule.

Around 10:00, I went over to M&B’s for coffee, a warm up, dog cuddles, and to borrow another 20lb tank.

I was all the way to town limits when I realised that I didn’t have my wallet! I had just put it in my coat pocket instead of taking my purse, something I’m normally smarter about. I had to drive all the way back home, retrace my steps to the garage, and then drive all the way back to town. So I lost another hour.

Unfortunately, M&B’s tank was expired and therefore got confiscated. I then discovered that I had a full 17lbs between my two seemingly empty tanks. I got a comment recently about propane freezing up in cold temps and I replied that I had never experienced temps cold enough to do that. Well, I apparently have!

Going to town for 27lbs of propane felt like a waste, but the propane guy said something that made the trip worthwhile: “Do you have an indoor place where you can store your not in use tanks?” Doh! I decided to keep my not in use tanks in the garage.

I got home mid-afternoon and the rig was at about 50F, having only gained 10 degrees. I was finally able to bolt down some food and then I had a nearly two hour long Skype meeting with a client about work for the weekend. And then, I had four hours of transcription to do by 9PM and I really wanted to get to Laura’s for cards before 8PM. So I typed for almost four hours straight, which was probably a record for me.

Just as I was heading out to Laura’s, I noticed that the air the furnace was blowing was getting colder. I switched off the furnace and exchanged the propane tank, which was still heavy, with one from the garage. For good measure, I put some blankets on the ground and then around the tank.

Card night was fun and Laura made sure I had carbs to burn to keep me warm through the night in the form of bread pudding and ice cream. I do believe this was the first time I ever had ice cream at 40 below. 🙂

I got in around 11:30 and the rig was at a toasty 60F. I went to bed with my iPad and watched a movie. At 1:30 I shut everything down, but as I was drifting off to sleep, I realised that something didn’t feel right. I got up and discovered that the furnace was blowing cold air. I bundled up, went outside, switched tanks, came back in, turned on the furnace, and made sure it was blowing warm air before going back to sleep.

At around 6:45, I woke up and again something didn’t feel right. I groggily got out of bed and sure enough, the furnace was blowing cold air. It was 52F in the rig, so it hadn’t been doing that long. I switched tanks and restarted the furnace a couple of times until I thought I was getting warm air.

I woke up again at 8:00 and it was evident that the temperature had dropped. I actually can’t remember if I switched tanks again or just cycled the furnace off and back on again. Whatever I did, I got hot air immediately and went back to bed till 10:45.

I got up to a rig at a pleasant 60F and decided to try to get to 63F. It’s been 45 minutes and I’m at 61F but… the furnace is blowing cold air again.

This is a furnace issue because I tried the stove at 6:45 this morning and I had no trouble getting all three burners going even though the furnace refused to blow hot air. So I don’t even know if it’s worth the trouble of switching tanks or if I should just turn the furnace off and on again.

Last night was supposed to be the last bad night, but it looks like we’ve got one more and then temps are going to climb steadily.

The situation has been challenging and I’m tired this morning, but last night was akin to stoking a wood stove all through a bitter night. If I had stayed at Laura’s, I would have come in this morning to a rig sitting at temperatures I wouldn’t be able to recover from easily in order to do today’s work.

What I find amazing is that I was fine to about -30, finding that temperature no more challenging than minus -20, which wasn’t that much worse than -10. I’ve always considered the magic number to be -10 and then after that it should be abandon ship time, but I’m revising that to -30 if I’m sheltered from the wind and plugged into shore power.

Well, I have hot air again, so it looks like cycling the furnace is all I need to do.

If I had traveled south this winter, I would still be in an area right now with unseasonably frosty temperatures, but without the ability to skirt myself in and where I’d have to pay big bucks to plug in, plus I wouldn’t have community support. I think I’m in the right place.

Beautiful frost pattern on the picture window.

Beautiful frost pattern on the picture window.