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Domestic CT Thermostat No Power


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Your Owners Manual shows this.... I highlighted and added some comments in red:

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The brown wire feeds power to the furnace from the fuse at the Converter under the dinette. There is also a yellow ground wire for the furnace under there, in a long ground bus (strip) on top of the frame, to the rear of the converter. You will see a bunch of yellow wires going into its screw terminals. You can check to see if they are all tight. The thermostat control wires (small gauge) go to the AC unit and then to the furnace, where it gets its power.

Most likely you have no power because the furnace fuse has gotten loose in its clips, or ears. They are really soft copper and can be bent out of shape easily. Remove that fuse and carefully squeeze the “ears “ a little closer together with a pair of needle nose pliers covered in electrical tape. Replace the fuse using the pliers, straight in, do not rock it sideways. Check the others while you are in there!

There is also a ground wire from the air conditioner to the ground bus in the “attic” cabinet (street side), that could be loose. The drawing is not at all clear about where the thermostat ground connects to the others......

If the fuse appears to be OK you will need to get a volt/ ohm meter and start doing some checks to see where there is voltage, and a ground, and where there is not. And there is always the possibility that the stat itself has failed, or a wire or connector has broken. You are going to have to do some exploring..... Good luck.

John Davies

Spokane WA

Edited by John E Davies
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"Mouse":  2017 Legacy Elite II NARV (Not An RV) Two Beds, Hull Number 218, See my HOW TO threads: https://olivertraveltrailers.com/topic/john-e-davies-how-to-threads-and-tech-articles-links/

Tow Vehicle: 2013 Land Cruiser 200, 33" LT tires, airbags.

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3 hours ago, Bobfirst said:

John do I need to shut off all power before removing the 7.5 A furnace fuse?

That is why I suggested using pointy pliers with an insulated tip, so you won’t short something out. If you have a plastic fuse puller you can use one of those for getting the fuse out. Unfortunately those clip onto the fuse to remove it, you can’t push one back into place with it, and it is too easy to cock it sideways when doing it with your fingers. And you still need to be able to get in there with pliers to squeeze the ears a little. Here is what it looks like, you can see the row of double ears that hold the fuses. Sort of hold them.... 

 

4CEF7EFD-60C8-4621-A251-3AE0C6644CC4.thumb.jpeg.5c9388364a34cd88a3660e8f25858c49.jpeg

I have no problem doing this, but when in doubt, disconnect the battery negative cable. Then, no worries. It is low voltage so not a danger to you, OTH do not remove the entire cover like in that picture without shutting everything down, the stuff on the right side is 120 volts and very deadly.

Something like this with electrical tape or heat shrink tubing works. If the battery is disconnected you do not need to insulate it at all. 

John Davies

Spokane WA

 

B172F7AA-7E35-46EC-A41E-88EF589B2F7B.jpeg

Edited by John E Davies

"Mouse":  2017 Legacy Elite II NARV (Not An RV) Two Beds, Hull Number 218, See my HOW TO threads: https://olivertraveltrailers.com/topic/john-e-davies-how-to-threads-and-tech-articles-links/

Tow Vehicle: 2013 Land Cruiser 200, 33" LT tires, airbags.

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2 hours ago, John E Davies said:

That is why I suggested using pointy pliers with an insulated tip, so you won’t short something out. If you have a plastic fuse puller you can use one of those for getting the fuse out. Unfortunately those clip onto the fuse to remove it, you can’t push one back into place with it, and it is too easy to cock it sideways when doing it with your fingers. And you still need to be able to get in there with pliers to squeeze the ears a little. Here is what it looks like, you can see the row of double ears that hold the fuses. Sort of hold them.... 

 

4CEF7EFD-60C8-4621-A251-3AE0C6644CC4.thumb.jpeg.5c9388364a34cd88a3660e8f25858c49.jpeg

I have no problem doing this, but when in doubt, disconnect the battery negative cable. Then, no worries. It is low voltage so not a danger to you, OTH do not remove the entire cover like in that picture without shutting everything down, the stuff on the right side is 120 volts and very deadly.

Something like this with electrical tape or heat shrink tubing works. If the battery is disconnected you do not need to insulate it at all. 

John Davies

Spokane WA

 

B172F7AA-7E35-46EC-A41E-88EF589B2F7B.jpeg

 

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I do not remember if it was the Heater/AC or HW Heater, but one was not working when at DCNP.  So I got to impress Wifey with my problem solving abilities, after her insistence and threatening me with "she was going to do it herself".  I mean I was on Vacation after all...

Some of the Fuses have a lip or ledge on the end with the rating #, so a fuse puller will grab/pull them quite easily.

Some of them are smooth or a straight bevel from the "Fuse Blades" back to rating #, so a "Needle Nose Pliers" works best.  Hint, use rubber coated N-N Pliers; it works on both... 

I did kill all Power because Electricity likes me more than I like it, and we only had had it for about 4 hours, and were still wondering what the !@#$%&? we got ourselves into... 

I did not notice before pulling the fuse if the "Fuse Blades" were set properly in the receivers on the Circuit Board.  However after removing and reinserting the fuse and re-energizing the electrical, the unit worked.   

I got off easy that day, Wifey was impressed, and it reinforced my confidence that we had made a very good decision in the purchase of an OTT.  

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Maggie & Bryan | Arnegard, ND | 2020 LE II (Twin Setup) Hull #665 | 2010 GMC 1500 ExtCab Sierra SLE 

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I don’t know anything about your disconnect switch, my trailer does not have one. Just try flipping that switch see if your other 12 volt stuff like lights and fridge go dead. All the fuses inside that box are fed by the same source, if one goes, the others do to. If that doesn’t do it, take off the negative cables coming from the inside of the trailer to your batteries, there are several. You don’t need to remove any of the jumper cables between batteries.

John Davies

Spokane WS

Edited by John E Davies

"Mouse":  2017 Legacy Elite II NARV (Not An RV) Two Beds, Hull Number 218, See my HOW TO threads: https://olivertraveltrailers.com/topic/john-e-davies-how-to-threads-and-tech-articles-links/

Tow Vehicle: 2013 Land Cruiser 200, 33" LT tires, airbags.

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John I pulled the 7.5 A fuse for the furnace and it was blown. Figured problem solved. Wrong! Immediately blew 2 new 7.5 A. Only the thermostat is not getting power. Any ideas what is causing the furnace fuse to blow?

I forgot to mention that the first blown fuse occurred while the electric heating strip was ‘on’. Could the heat strip be the continued cause of blowing the fuses? Can the heat strip be removed from the Dometic A/C?

Edited by Bobfirst
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The furnace fuse could be blowing for several reasons, the most likely IMHO is a bad motor or a jammed fan. Do you have insect screens on the outside vents? Wasps can get inside and block the burner can. If the combustion fan is jammed by a nest, that would sure do it. Or the motor has simply failed. Or the positive wire has grounded out somewhere, or broken and shorted.

A simple next step might be to disconnect the power wire at the furnace, see if it still blows the fuse. If it does, then you know the motor is (probably) OK. 

Lots of possible reasons. None are real easy to isolate. You need a multimeter, and then you can start troubleshooting the wiring. If you are not comfortable with that, get some help. You may need to do a resistance measurement through the motor windings, and maybe “ring out” the actual wires to see if they are attached correctly at each end. Whatever happens do NOT replace the 7.5 A fuse with a higher rated one. The repeated fuse blowing is telling you that there is a serious problem. The purpose of a fuse is to protect the wires, not the part at the other end. Put a great big fuse in that slot and you will have a fire as your wire melts.....

Good luck.

John Davies

Spokane WA

 

 

Edited by John E Davies
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"Mouse":  2017 Legacy Elite II NARV (Not An RV) Two Beds, Hull Number 218, See my HOW TO threads: https://olivertraveltrailers.com/topic/john-e-davies-how-to-threads-and-tech-articles-links/

Tow Vehicle: 2013 Land Cruiser 200, 33" LT tires, airbags.

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  • 2 weeks later...

John,

"You need a multimeter"

Any suggestions, first for Oliver applications, then if I must... Household applications.

Maggie & Bryan | Arnegard, ND | 2020 LE II (Twin Setup) Hull #665 | 2010 GMC 1500 ExtCab Sierra SLE 

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For RV use I recommend this one.

https://www.amazon.com/Uni-T-B4Q094-UT210E-Current-Capacitance/dp/B00O1Q2HOQ/ref=sr_1_1?dchild=1&keywords=Uni-T+B4Q094+UT210E+True+RMS+AC%2FDC+Current+Mini+Clamp+M+W+Capacitance+Tester&qid=1609729532&s=industrial&sr=1-1i

It does most common measurements like voltage and resistance, but the most useful feature is the clamp on ammeter. You can use it to measure current without disassembling any wires, though they do need to be separated from each other, not inside a loom or harness cover. For checking your electric trailer brakes it is WONDERFUL. I liked mine so much I left my regular multimeter at home, and gave one of these inductive ones to my son for Christmas.

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Look through this page to get an idea of how it is used for measuring amps.

https://olivertraveltrailers.com/forums/topic/2685-how-to-brake-wiring-is-undersized-some-answers-and-partial-solution/

You can use it at home, but really a plug in outlet/ gfci (ground fault) tester with LED lights might be more useful, and it would also be very good for checking a campground electrical post before plugging in....

John Davies

Spokane WA

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"Mouse":  2017 Legacy Elite II NARV (Not An RV) Two Beds, Hull Number 218, See my HOW TO threads: https://olivertraveltrailers.com/topic/john-e-davies-how-to-threads-and-tech-articles-links/

Tow Vehicle: 2013 Land Cruiser 200, 33" LT tires, airbags.

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