232rbw furnace won't fire on battery

TweakerG · 09-29-2020, 04:58 PM

I just bought a used 2020 232rbw and the heater was working when I went to look at it, but they must've had it plugged in to shore power because I just can't get it to work on battery, but it works fine on shore power. The fan will kick on for about 30 seconds and then stop. I can't hear it trying to light like I can when it's plugged in. I thought maybe the batteries didn't have enough juice so I replaced them with two known good ub121100s that I got from work. Still won't work on battery. Any ideas? It has the Dometic furnace under the jacknife couch, which isn't too easy to get to.

TweakerG · 09-30-2020, 10:18 AM

I just wanted to update in case anyone is having the same issue and comes across this. I tore in to the furnace to see what was happening and in my case I think it's the sail switch. I tested the switch and it tests fine, but the fan runs just a touch slower on battery than it does on shore power so it seems like on battery it's just not enough. I put a very slight bend on the end of the fin that goes to the switch so it has a millimeter or two less to travel and it's working now. I ordered a new switch for a Hopefully more permanent fix as it seems the sail kit switch comes with an upgraded mount.

Route 66 Traveler · 09-30-2020, 10:39 AM

Have you measured your battery voltage when the furnace is running? Are you running two batteries or just one? Sounds like you barely have enough battery power to operate the furnace...doubt if it would last all night.

TweakerG · 09-30-2020, 02:04 PM

I'm running two batteries. Showing 12.5 volts while the furnace is running.

TweakerG · 10-03-2020, 08:25 PM

Well scratch that on the sail switch fixing it. It's still really intermittent even after putting in the new sail switch. I hooked my multimeter up to the splice right before the furnace and I get 12.7 volts, but when the heater kicks on that drops to 12. With it plugged in to shore power I'm seeing 13.2 while it's off and 12.5 while it's running. I've checked all of the connections that I can find and I'm not sure where that .7 volt drop is coming from.

TweakerG · 10-04-2020, 09:21 AM

I also noticed if I take the two 4" flex ducts off the furnace then it runs just fine. Even as low as 11.5 volts. There is nothing in the ducts causing reduced air flow though and the manual states that's what it needs is two.

RogerR · 10-04-2020, 09:42 AM

.7 volts drop seems a little much. Is there a way to run a new wire direct from the panel to the furnace with no connections in between? You might have a bad scotch lock connector or just a poor wire connection. First I would take the wire off both ends (panel and furnace) and make sure each connection was clean and tight.

TweakerG · 10-04-2020, 10:01 AM

I'll see if I can get back in there somehow. The panel shows the fridge and furnace are on the same fuse. From there it goes in to the cabinets and I can't find where it goes from there. It is only getting a .2 volt drop at the panel when the furnace is on, which is the same thing I'm seeing at the battery.

TweakerG · 10-04-2020, 08:53 PM

Quote:

Originally Posted by RogerR

.7 volts drop seems a little much. Is there a way to run a new wire direct from the panel to the furnace with no connections in between? You might have a bad scotch lock connector or just a poor wire connection. First I would take the wire off both ends (panel and furnace) and make sure each connection was clean and tight.

I pulled the panel off and checked some voltages. I started off with a battery voltage of 12.6. Under load that drops to 12.4 at the battery and at the panel. I took the panel off and I have the panel wire, furnace positive, and fridge positive in a wire nut. The negative goes to a bus bar and then to ground. Everything checks out at 12.4 at the panel. I tested from panel positive to the negative at the furnace and I get 12.2. Negative at the panel and positive at the furnace I get 12.2. So I'm dropping 2 volts on both the positive and negative between panel and furnace. Checking from negative at furnace and positive at furnace is, you guessed it, 12.0 for a drop of 4. I'm wondering if there is something in the wall causing both of those wires to drop 2 volts. There are no scotchlok connectors in there. I did notice that I'm seeing 2 volts on the positive when I disconnected it from the panel to redo the wire nut just in case. Although that was still with the fridge and furnace still twisted together so I don't know if it was coming from the fridge or the furnace.

TweakerG · 10-05-2020, 10:19 AM

I decided to test the resistance on the cable today so I cut off the splices at the furnace, wired the positive and negative together and check the resistance at the panel. Everything looked good. I started looking at the splices they used and they were awful. More than half of the wires from the cable going back to the panel were cut off on both the positive and negative. Put everything back together with good splices and my furnace is working now even with my battery at 12.4 volts. I'm going to see how low it'll go before the furnace stops working, but I'm hopeful that it's fixed.

TweakerG · 10-05-2020, 09:57 PM

Just updating in case anyone comes across this looking for help. Furnace has been working great now. I ran my batteries as low as I dared let them go and furnace still lights. Those terrible splices from the factory were my problem the whole time. On the plus side I now know every single part of the furnace in case anything else ever goes wrong.

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