12V to fresh water tank heater questions

msutoad

Senior Member
Joined
Jul 19, 2021
Messages
380
Location
NC
Hey everyone, it’s been a while since I have posted…. Hope you all are well.
I need some help/guidance. Reminder, my rig is a 2023 Mo 397TH. I came home Tuesday from Myrtle Beach and it was cold. My furnace worked fantastic, and we enjoyed being at the beach regardless of the weather…. I had he tank heater on for one night because it got down to 20 degress. I turned off the tank heater and the furnace, we pulled home, all is well. Prior to going to bed Tuesday night, I went to check the furnace was working fine since it was going to be 20 degrees again, and I was too lazy to winterize after getting home. I had planned to turn on the tank heater too. When I tried to turn on the tank heater it would not stay on. I checked power from the inverter, and the 12V side, all was working and putting out power. I tried to turn on the furnace, and I could hear the one connect system clicking attempting to turn on the furnace, but it would not work. I tried to turn on the heat pump for grins, since I have 50AMP service at home, NOTHING…

I started taking the furnace apart to see if maybe something happened on the trip home. No power was getting to the furnace when I grabbed my volt meter. I went to the panel, and the furnace fuse was burnt. So I replaced that, and foolish me I tried the tank heater again, and it instantly popped the furnace fuse… FRUSTRATING… I replaced it again, and tried the furnace and it worked, and so did the heat pump. Why does the 12V fuse have anything to do with the heat pump which used 110V? And why is the water tank heater not on its own 12 fused leg so that ONLY the furnace is on the labeled fuse leg ? Is this normal, and do others have this same setup? I have 5-6 unused fuse legs so I could have dedicated connections I think if I re-wire it. Wondering what some of you experts think about this. Also, the water tank heater pops that fuse instantly still, but did work for one night, so what could have happened to that system to be broken after one night of use? Looking for ideas here too please. Thanks in advance.

Jason
 
Hi Jason. I suspect that for some reason that tank heater developed a short. Either in the heat pad itself or in the wiring somewhere between the pad and the fuse panel. If I had to guess - the pad. The furnace is 12V so it does make sense that if they share the fuse, neither works once you turn on the pad and blow the fuse.

The heat pump, I'm not so sure. But somehow it must be on the same circuit. Perhaps the thermostat is wired to that circuit so if the thermostat doesn't have power the heat pump doesn't work?

All that said, not sure why they would wire everything to one circuit. My unit didn't come with heat pads so I installed my own and ran each to its own fuse and switch. I would definitely suggest going that route with yours.
 

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