Refrig 12 VDC 20A fuse blown

A second problem we ran into with our trip this week was that our refrig wasn't keeping cool when we were driving; it would run fine on 120VAC or propane, but we would gain 10 degrees or more on our driving days which hasn't happened before, even in 90 degree summer days. Once we spent enough time in one place for me to poke around, I found that the 20A fuse was blown in the back of the refrig (so not the automotive blade fuse in the converter on the bathroom wall, but the glass fuse that you get to by digging into the outside panel in the bottom rear of the refrigerator).

More interestingly, I found that the white 12 gauge wire to that fuse isn't white anymore, but yellow-brown from heat. In fact, it took me a while to convince myself that it wasn't miswired with yellow wire. Anne and I had been using the propane and 12VDC settings on the refrigerator, and hadn't been using the 120VAC setting, with the theory that we would be less likely to forget to reset it to battery when we were leaving a campground, but it's possible that this was a bad idea (aside from some efficiency loss in the converter).

Anyway, I replaced the fuse, and used it on battery only when driving. We had to drop the TM off at The Car Show for the furnace to be looked at anyway, so I will post an update if they find anything (like a 12VDC heating element that has too little resistance or something like that).

[Bill]

The Car Show is a good outfit, so they will find the problem and correct it. In the meantime, let me comment that the #12 wire is more than sufficient to carry the current to the refrig, so I conclude that some other source of heat is discoloring the wire. Perhaps it is too near the chimney?

I'm not sure why the wire is white - I would have expected black - but my TM is closed up in the garage at the moment, so I can't offer anything constructive in that area.

By the way, some (but not all) tow vehicles do not provide sufficient electrical power to the TM to run the refrig while towing. My 2002 Explorer (which should be similar to your 2003 Expedition) was one of them. The Search tool should uncover my none-too-polite post on the topic, in about 2003.

The original post has apparently been lost, but here is a follow-up.
http://www.trailmanorowners.com/foru...ead.php?t=4909

Bill

[wbmiller3]

Our 2003 Expedition runs the fridge just fine while towing. May just be a lucky choice of options.

With the new fuse from Radio Shack in place (and 3 extra's now in the drawer), the refrig worked fine the way back from Texas, and the battery looked normal at the end of each day's drive. So I think the Expedition's wiring is probably good enough.

The Car Show thinks that the variance of the 12 VDC heating element is enough that the browning of the wire should be considered normal with that much 12 VDC usage. Remember that throughout this year up until this trip we didn't bother using the 120 VAC setting on the refrig, instead leaving it on the 12 VDC setting so that we wouldn't accidentally forget to switch it over when we disconnected from shore power. Also, when connected to shore power, I had 14.1 VDC with the converter doing it's job. The heating element is just a resistor; at 12 VDC it draws 12A but at 14 VDC it draws 14A which is higher than what it will draw while driving at closer to 12 VDC.

So my lesson learned is that the 12 VDC setting is adequate for driving but I should either use the 120 VAC setting or propane (their recommendation, and also the recommendation of other RV dealers I've spoken to when I've rented RV's in the past).

If the element draws 12A at 12V, that's a 144W element. If you raise the voltage to 14V, it should only draw 10A I think. If you have a brown out and the voltage drops to 6V, the unit will draw 24A and blow the fuse. That's my guess anyway.

The back of the on-line manual says 12 Amps at 12 Volts DC and 14 Amps at 14 Volts DC, so the resistance is constant at 1 ohm, not the power consumed.

Ah that makes sense. It is a resistor after all. More voltage, more heat, more watts then. And not linear as it draws more amperage as volts goes up.

So you'd have to get to 20V before you burn out a 20A fuse, basically. Unless you have a short somewhere which is zero ohms resistance and 12V / 0 is a lot of Amperage, HAHA.