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Old 12-20-2010, 04:45 PM   #1
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Blown Refrigerator and Furnance Fuse

On the last day camping this past weekend our TT furnace/fridge 12v 15amp fuse blew. The whole weekend we ran both the furnace and the fridge with out problems. We were connected to shore power. Didn't think it would be much of an issue at first, was prepared with spare 15amp ATC fuses. Quick fix, I thought. But it wasn't to be.

Not too sure of the steps to follow when replacing a fuse, I turned off both appliances, tripped the main circuit breaker in the TT distribution center, disconnected from shore power and disconnected the TT battery. All dead inside, no power anywhere. Replaced fuse, reversed the steps, shore power back on, battery back on, however by the time I got to the distribution center (even with the appliances still off) the new fuse was already blown. Not to be discouraged, I repeated the steps with a second fuse, same results.

Tech details:

TT is a 2011 FR Rockwood 2702SS
Dist Center is a CHENG WF-8955PEC
Furnace is a Suburban NT30SP 12v DC
Fridge is a Dometic DM2652RB (Gas and AC), however it needs 12v for control panel

The obvious (to me at least) is that some sort of electrical short must have developed over the weekend. Again both the furnace and the fridge ran w/o problems (cycling on/off normally) from Friday until Sunday night. The fridge and the furnace share a single 15amp ATC style DC fuse on the DC panel, (the fridge also has a 15amp AC breaker which didn't trip) so once the fuse blew both appliances quit working.

I'm well within my warranty period so I'm not too concern, however we are planning a couple more trips before the year is out so I can't afford to have it at the dealer. (I'm also smart enough to know the limits of my ability and not make a simple problem worse!)

I'm currently reviewing installation manuals for the dist center, furnace and fridge to identify the electrical connections. My idea is to isolate the two appliances from the distribution panel (and fuse) and determine which one is faulty. I can compensate without the furnace, but no so without the fridge.

Sorry for the long explanation, any help suggestions would be greatly appreciated.

frank
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Old 12-20-2010, 11:38 PM   #2
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Wow, this is a head scratcher.

I would start by isolating as much as I could items on that circuit and have plenty of 15 amp fuses on hand.

Unplug the fridge from AC and remove the 12 volt dc red lead from the converter to the fridge. You will need to use a small screwdriver to remove it from the back side of the 12VDC terminal block. Tape it with electrician's tape to ensure it does not short out. That should remove the Fridge as the source of the short circuit.

Operation & Installation Manuals - Dometic

The heater should also be isolated by removing the red 12 VDC lead and taping it. Install a known good fuse and restore battery power. If the fuse blows again, you have eliminated the appliances as the source of the short. You have either a pinched wire or a failed converter.

A quick way to check the converter is to swap the power leads to an adjacent 15 amp dc circuit. If the fuse holds on the formerly bad circuit and the problem moves to a the new circuit, its in the wiring. If it stays on that fuse it is the converter.

If the fuse is good after eliminating the two appliances, then connect the heater only. Restore power. If the fuse holds the problem is the fridge control board. If it blows its the furnace control board.

Good Luck. If this seems over the top.
Make an appointment at the service center.
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Old 12-21-2010, 12:26 AM   #3
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I have seen "auto reset" circuit breakers that will plug in where an ATC fuse goes. These can be used to replace your fuses. They were around $6.00 each, in different sizes. May want to get one 15 amp and use it till this problem is solved. May be cheaper than a several fuses. Check Carquest, and your camper dealer.
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Old 12-21-2010, 08:34 AM   #4
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I do not recommend auto-resets for a fuse that trips for an unknown reason. He has a short in the harness or appliance somewhere.

After troubleshooting, if he determines that the fuse rating is too close to the load (and not a dead short somewhere); an autoreset would be the logical. I use autoresets for my slide fuses and my stabilizer and landing gear circuit protection. If the slide gets water between the slide and the wall, the ice that forms in the dead of winter can blow the fuse when I try to open it. In this case the fuse is (was) hard to get to and I knew why it tends to blow. Same issue with the rear stabilizers (electric); if I bog the motor to set the legs the fuse can blow. It is another hard to change fuse. Ditto on the front landing gear.
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Old 12-21-2010, 08:45 AM   #5
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IF a fuse is blowing before the fused devices are even turned on
the short might be very close to or inside the fuse box.
IF you're in warranty this is one for the dealer.

It's also possible that a wire is pinched or burnt in the furnace.
It could blow the fuse even though the furnace thermostat
has not been turned on.
I would remove the furnace and look for a mis-routed wire
in that area. It probably is too close to some hot part of the
furnace and has been melted thru.

This is just a guess but a good place to start.
Good Luck!
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Old 12-21-2010, 12:12 PM   #6
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Thanks everyone for your replies and suggestions. winderider, the auto resets fuses are a good suggestion, and will definitely swap out a couple of ATC fuses for them, but just like herk7769 points out let's find the culprit first.

herk7769, instead of disconnecting the appliances at the appliance end, as you suggested, my thinking was on isolating the faulty appliance by removing the distribution panel cover and disconnecting (what I was expecting to find) the two 12v leads for the fridge and furnace connected to the same bus. Then reconnecting one at a time to find the faulty one. However my "idea" will likely be proved wrong as I just got off the phone with our dealer's RV technician and he indicated that he will very surprised if FR wired two leads directly to a single bus. He said that what I will most likely find is one lead connected to the panel bus (where the fuse is) from there the wire goes to the 12v block behind the fridge (the 12VDC terminal block you refer to in your post), from there I should see three positive (red) wires: one for the fridge's control panel, one for the fridge's gas solenoid, and a third one (he said it should be red/white) for the furnace. Note: The tech was going on memory along and he did indicate that for every model he's seen a different installation method. Of course seeing it in person is necessary for a final evaluation.

From here all that is left is isolating the problem appliance and hopefully getting the fridge back working. Let me know what you guys think. The rest of the problem I'll leave to the dealer to fix.

Again thanks for all the replies, it is reassuring you guys are here looking out for the rest of us. I'll post an update.

frank
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Old 12-22-2010, 04:45 PM   #7
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UPDATE. Was able to work on isolating the faulty appliance today and as expected (and hoped for) it turned out to be some type of electrical short inside the furnace. In reading the install instructions for the furnace the connection is a pig-tail type connection @ the furnace, that's what I ended up disconnecting (vs the 12v connection at the 12v block behind the fridge) The fridge is well now, which was my priority, I'll let the dealer deal with the furnace after the first of the year.

Thanks to all and happy holidays!!

frank
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Old 12-23-2010, 08:11 AM   #8
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Great! There's lots of hot surfaces and sharp edges in a furnace.
It's easy for a wire to be mis-routed and get melted or cut.
Glad you found the culprit and THANKS for the follow up.
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Old 03-15-2011, 09:28 AM   #9
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UPDATE: The furnace unit was replaced with a new unit by the folks at Tropical RV in Ft. Pierce, Fl. The old unit is being shipped to Suburban for them to figure out the problem. The furnace replacement and a couple of other minor things, I was heading home within two hours! Great service!
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