RV Furnace Troubleshooting Tips and System Overview

The furnace in your RV is very similar to the one in your home. There's not a whole lot of maintenance that's required of it, but there are some things that you need to know to make it run more efficient and for troubleshooting purposes. Now, the furnace in this one, this happens to be a 2003 Brave and we're gonna take this cover off here the backside and we can see that we've got a suburban model in this one and we've pulled this one out as an example of what we have. And this runs off of the propane, we've got our liquid propane system in here gonna be supplied by the gas valve down in this area in here. And the way the system works is once you have your thermostat set to the desired temperature and it calls for heat, it's gonna go through the circuit board, which we see on this unit here is gonna come into here and it's gonna start the fan to start with. So this fan motor right here is gonna spin. And we're gonna take this off just so we have a little better understanding of what's going on in here. So we've got our fan here. And so the first thing that's gonna happen is nothing's gonna start. There's no flame, there's no heat that's gonna happen, but the fans are gonna kick in and the first thing it's gonna do is it's gonna get any exhaust or old air out of here. And the thing you gotta remember about the system is it's gonna actually draw air from the inside and heat it, it's not gonna draw air from the outside. A lot of people think that that's the case, but it doesn't. So the first thing it does is it bows this in. It's gonna kind of clean everything out. And what it's also looking for is it wants to make sure we have proper fan speed, proper voltage coming in. And we have right here, this is called a sail switch. And it's gonna be sitting more like this on the other side of it. But we need enough fan speed and airspeed to lift this and you hear that little clicking in there. What that's doing is it's saying, okay, I have enough airspeed, I have enough voltage so everything else is gonna work properly in here because it's pushing this up and closing that circuit meaning the voltage can go through and tell everything is good before it starts to light the burner assembly. So then right here we have inside this then we can see this little light on the inside of it. This is where our spark igniter is in our burner assembly And it will then open the gas valve once this says, yep, I have enough speed, I have enough voltage it's gonna start the flame on this thing and then it'll light our burner and it's gonna draw air again from the inside and just run the air through this system here and out to your registers. So the other thing we wanna look at is on the backside of this. We have a thermal coupler or basically a temperature sensor. And what that does is if this gets too hot, then that's gonna again, open and say, nope, we have problems. We're getting too hot. We're gonna shut the system down. So the whole thing will shut down. And a couple of things that you need to be aware of, on the inside of your rig, you're either gonna have a plenum like this one runs all along the inside and it's got the duct work in the floor just like you would in a home or you're gonna have a series of what we call elephant trucks, and they're the, trunks. They're the corrugated hoses that go underneath cabinets, underneath the sofas and come out in areas. So you need a good air flow in both of those systems to make sure that this doesn't get overheated or that it's pushing back air and we're not getting enough air flow over that sail switch. And a couple of things that happen is a lot of people like to put rugs down on the floor because they got dogs and wooden floors or they don't wanna get their carpet dirty or ruined or worn. So they put runners or carpet extra. If you plug those vents up inside that RV, then you restrict the air flow. And that airflow then means that this is gonna heat up, either our temps switch is gonna shut the system off or our sail switch is gonna shut it off. Same thing with our corrugated hoses, if you start storing items in your cabinets, underneath, and you start pinching those. I see a lot of people that don't realize that by shoving something up in there and forcing it in you kink that hose now you don't have good air flow going through that hose. So again, we're gonna get either overheating on this side or we're gonna get that sail switch that is going to open the circuit and say, nope, we can't run. If your unit isn't running, there's a couple of things that we look at. The first thing is you've got to make sure that you understand that these run off a 12 volt system and you need at least 10.5 volts for this fan to go fast enough to open that sail switch. And this is a very common problem. We hit on this over and over again with just about every appliance that runs off of LP is if you have sulfated batteries, this might start up and run for 15, 20 minutes and it works pretty good, but it's gonna draw some really good power out of those batteries. And if they're sulfated, they're gonna drop really fast and if you don't have at least 10.5 volts, this fan is not gonna spin fast enough, the sail switch is gonna drop and it will shut the system off. But it only shuts off the control module and the LP side, your fan continues to run. And so that's kind of the deceiving part is a lot of people say, well, my fans running so I got plenty of voltage but I'm getting cold air. If the case then more than likely, you've got low voltage enough that it's not getting that sail switch up and it's not closing the circuit meaning allowing the voltage to go back in to tell the control panel. So there's not a whole lot of maintenance that's required on these other than to understand the voltage. And one of the things that I do tell people, okay, if you and they say, well, I'm plugged in and I still have cold air coming out and the fan running. If I plugged in, I got battery power. And that's not always the case because when you're plugged into an outlet at a campground source, you have a converter that is charging your batteries. And some of the older units I've seen actually where there are so much stuff being used, like the air conditioner, which you wouldn't use air conditioner and the furnace at the same time. But if you're using a lot of appliances inside that are drawing, you have 30 amps in that circuit. So your refrigerator draws about six to eight. Your air conditioner is gonna drive about 14 or 15 amps. All these other things, there's not a lot of amp draw left for that converter to charge that battery. And I have literally seen in some units where you're plugged in and the battery still drain because it doesn't have enough power to keep them going. The other thing that a lot of people don't realize is that your batteries are gonna start off at 12 volts and the converter should shut off when it's fully charged. And as it drains down, it gets to a point where now all of a sudden, the converter says, Oh, I'm at 10.5. I'm gonna kick on. So it's not on all the time otherwise it would probably boil your batteries and fry them out. So you got that little area in between where sometimes it drops to 10.5, that says it's too low. The converter hasn't kicked on so there could that small little gray area where I still have low battery power even though I'm plugged in. What I tell people if they're plugged in and this is not running or it's running but it's blowing cold air, put a battery charger on. Just in addition, put a battery charger, give that boost on the battery. See if that makes a difference. That will immediately tell you that it's the battery. If it doesn't help, then you come back to here and you look, is it the sail switch? Did that go bad? Is it the thermal coupler back here, the temperature switch, did that go bad? Or it could be a module board. Then you started getting into some heavier diagnostics on some of this stuff. There are some videos that dig into a lot heavier, but that's the basics of how the system works, what you need to understand about air flow and voltage to make this system work and to keep you warm.