Furnace works on 12v but not on AC...??

[Heddy]

Here's a description of how this has gone down (apologies for the length):
Both A/Cs and the furnace were working fine a few weeks ago. Then.... on Sept 26, we took our 5 month old Avalanche to a dealer shop for warranty repairs. While at the shop, the Avalanche was winterized because temp went down to about 26 degrees for 3 nights. Picked up the Avalanche on Oct 22nd and immediately drove 9 miles to campground, hooked up to the shore supply and de-winterized. First attempt at the furnace and it didn't work. After checking around, it was the glass fuse on the thermostat board that had blown. Replaced it. Turned on the rear A/C and the same glass fuse blew. Replaced it again. Turned on furnace while hooked up, it immediately blew the 15A fuse next to the breakers in the camper. Shut down the shore power. Furnace works fine when on battery power, but blows fuse while hooked up. Got out volt meter and checked several things. Voltage appears normal at batteries, AC wires coming in at breaker box, and wires coming in to 12v side of breaker box.
Thoughts on what the heck is going on?

[NH_Bulldog]

We can probably narrow the problem down to the AC power side of the system, since the 12v DC system works when not connected to shore power. The two sides connect to each other through the converter. That being said, you first need to validate that your shore power connection is proper. Do you have an EMS (Electrical Management System)? Not a surge protector, but an EMS that will analyze the incoming power BEFORE it gets to the camper and keep power disconnected if a fault is sensed. In lieu of that, you at least need a plug-in circuit tester (they make them for standard electrical outlets as well as 30A and 50A RV outlets) Before you do anything else, you HAVE to verify that the shore power source is correct.

AC power comes in to the RV from the shore power cord and feeds the power center, which in turn feeds the AC side of the system. The power center also passes power to the converter (which converts to 12v DC to run things like lights, slides, jacks, furnace, etc.). On newer/larger models, the converter simply plugs into an outlet on the back of the power center with a regular cord and plug. So with the 12v items known to be okay when on battery, working backwards we would look at the converter. The next step while connected to shore power (once you have confirmed that it is a good power source) is to flip the converter breaker in the power center to the off position (or if you can get to the converter, unplug it from the back of the power center), then try out the furnace, the AC, etc. and see if any fuses blow. If everything works, it is likely your converter, but you first must confirm that your shore power connection is correct.

I use a Hughes Power WatchDog EMS/EPO. It has an app where I can monitor my power conditions. It will also prevent power into the RV if there is an issue. On a recent trip, we plugged into the 50A outlet at the pedestal and there was an open ground error, so I tested the 30A outlet and it read fine, so we used that without any issues.

[Heddy]

Thanks for responding Bulldog!

We do have a surge protector that includes a circuit analyzer and it is saying there is nothing wrong with with the shore power (no missing voltage, no line & neutral reversal, no open ground or open neutral).
I went through with your idea of flipping the breaker for the converter and trying all of the electrical things in the rv. With that breaker turned off, everything worked.....except the furnace. Because the rear A/C also worked (it also was blowing the fuse when turning on with shore power), it seems like the converter is an issue. But not sure if that repair will solve the furnace issue. What do you think?

[chuckster57]

I would be looking at the AC control box.

[Stumpy75]

Originally Posted by Heddy

Then.... on Sept 26, we took our 5 month old Avalanche to a dealer shop for warranty repairs.

What was it in for?

[Heddy]

The water pump was acting up. When we picked it up the service guy told me that a valve setting on the pump had to be changed. Also, they straightened out a grey water valve and now it opens and closes...better. Lastly, the tank level indicator lights seemed to be off. The repair report says "CAUSE: Removed and installed pull cable correctly." The only other things that also happened is winterizing and sealing cracks on the roof. It doesn't seem like any of those specific matters would've had an effect on the furnace. But i could definitely be wrong.

[firestation12]

I’m confused with the intermixed terminology. A furnace to me is the propane powered floor level heating system. The rear ceiling mounted air conditioner works off of shore power 120 volts, and If it also contains a reversing valve, the rear air conditioner can also be described as a heat pump. A heat pump would not work unless connected to a source of electricity. The rear unit would not be considered a furnace. Is the op describing the rear unit as working on battery but not AC or the term AC being used as alternating current instead of air conditioning?

[rlh1957]

The furnace is 12V DC only. As long as you have 12V available furnace runs. There are fuses for the thermostat which is 12V & fuse for Furnace, no breaker.
Could be a wiring issue if shore power going to converter causes converter 12V output to interfere with rig battery power. Converter or wiring is suspect.
What recent rv shop work has been done? What recent work has been done or added?