# Fuse Blows On Thermostat



## spidey

Camping for a month this summer and had the fuse blow on the thermostat. We have a 2011 Outback 250rs. We have been mostly using just the fan since the nights aren't cool enough for the furnance. One night when we did need to use the furnace I saw a flash and the new fuse I replaced went. It works fine on the fan setting with a new fuse but as soon as you put it to heat it blows. I haven't tested ac since I'm on 15amp. Everything was fine this spring when I tested everything. Thankfully we have a space heater for cool nights. But who else has had this issue.


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## CamperAndy

Actually this is a new one for me. First I didn't know there was a fuse in the thermostat and I have never heard of one blowing. Which makes sense as if I had heard of one blowing then I would have heard there was a fuse!!

The only reason for a fuse to blow like that is a short in the wiring to the heater or a failed control board on the heater. I would test the wires to see if any of them are grounded.


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## spidey

How do you test wires if they are grounded. I won't be doing any of this until its at home. How does a person test for a failed control board. Do they just go like that.


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## CamperAndy

Sorry for the slow reply, been camping!!

Grounds are easy if you have a volt meter. Lift the wires between the thermostat and the heater control board and check resistance to ground and to each other. For the control board, yea they sometimes up and die, unfortunately I know of no may for a layman to test without replacement.


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## spidey

CamperAndy said:


> Sorry for the slow reply, been camping!!
> 
> Grounds are easy if you have a volt meter. Lift the wires between the thermostat and the heater control board and check resistance to ground and to each other. For the control board, yea they sometimes up and die, unfortunately I know of no may for a layman to test without replacement.


You make it sound easy, a lot of that is greek to me. 

Lift the wires where, at the furnace? I can get access by removing the jack knife sofa, but if the issue is in the walls then what? How do you check resistance to ground with a Volt meter? I do have one.

These are the things that make me NOT want to own a trailer anymore, been throwing the idea around for a few years, getting tired of fixing things, seems thats what all my free time ever is is maintenance and repairs.


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## CamperAndy

It is a house on wheels and you have to maintain the house.

To check for ground with a meter. Lift the wires at the thermostat and the heater control board.

Set meter to resistance and touch one lead to the wire and one to the metal frame of the trailer, should be O/L or infinite resistance. Check each wire to ground. then check wire to wire for a short between the wires. If the issue is a pinched wire in the wall then you will have issues pulling replacement wire.


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## spidey

CamperAndy said:


> It is a house on wheels and you have to maintain the house.
> 
> To check for ground with a meter. Lift the wires at the thermostat and the heater control board.
> 
> Set meter to resistance and touch one lead to the wire and one to the metal frame of the trailer, should be O/L or infinite resistance. Check each wire to ground. then check wire to wire for a short between the wires. If the issue is a pinched wire in the wall then you will have issues pulling replacement wire.


Ya i know, and I do maintain and maintain. Still doesnt seem to matter when things still break, expecially something like this. This plus some water damage on the back slide (again) is going to eat away at 2 entire weekends or more

I already have a house, thats why Im considering getting out of the RV game. People are havign fun on weekends, Im fixing random crap like this  As Im getting older, Im getting rid of things that take up my free time. Things that break, I weigh the options of repair, or just get rid of it and not replace.

I think this may be a take it in thing. How can I touch the metal frame of the trailer from the inside at the thermostat? Wires are soldered right onto the board at the thermostat, how do you lift those.

Sorry this shit puts me in a bad mood, all my free time consists of is repairs. Even reading this forum, things are happening to their trailers now matter what they do to maintain. Even some that think they are doing the right thing is wrong. The front cap issue as an example

If it does come to pulling the wires, that will end the fix and use a space heater.

Thanks for the help though


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## CamperAndy

I understand your frustration. I camp with several different people on a regular basis and actually help each other as part of the get together. We all learn and things get fixed. It takes the stress out of the issue more often than not.

Good luck.


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## spidey

Well worked on this yesterday, after a few test and more fuses blowing, I dont know what else to do. Replace the thermostat maybe is the next option. No wires I could see are rubbed bare and shorting, the blower fan isnt siezed or stuck. So kinda at my wits end. Has to be fixed, even if we dont use it much, since when we go to sell it eventually, dont want to just pass the problem along


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## spidey

ob277rl said:


> Spidey I will go along with CamperAndy and say I am not familiar with a fuse in the thermostat itself. If you can post a picture or two of what you are working on it might help. Good Luck.
> 
> Robert


I took pictures yesterday of the wiring, but forgot to take it of the thermostat itself.

Its a Coleman-Mach thermostat, Model AP7862

Ill take some tonight and post. Going to go to an RV place after work and just ask some questions. And a guy at work is going to help me with my Ohm meter so I know what to do.

I did narrow down on the Coleman-Mach website what wires are for the furnace only. I have 6 wires connected, 4 are grouped together and splt up from a big brown wire, those are the A/C. The other lone two are for the furnace


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## spidey

ob277rl said:


> Spidey as I changed out my analog thermostat early on for a digital one, I haven't had much experience with the original unit. But I do still have the original one and low and behold there is a 2A glass fuse in there. I found a thread on RV.Net Open Roads Forum: that is about the same problem you are having, maybe it will be of some help. Good Luck.
> 
> Robert
> 
> http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/27728529.cfm


Thanks, glad you were able to prove it was there. I think some people thought I as crazy.

I read that yesterday as well. The fuse only blows on furnace, fan hi and low work fine. I didnt test AC yet since I only have 15 amp.

I am hoping it is just the theromostat. if its an "in wall" issue, I dont think Ill be repairing i, might be a take it in problem.

I wish I could find someone with a thermostat I could test. Dont want to buy one and its not the issue


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## spidey

ob277rl said:


> Spidey when I changed out my thermostat I realized that the wiring from the thermostat is permanently connected to it. In the wall it connected to the trailer wiring and the color code of the trailer wiring was whatever they had handy at the time. Before I removed the original thermostat I used masking tape and a felt tipped pin the mark the trailer wiring to match the thermostat before disconnecting it. I had to pull the slack on the wiring in the wall to find the crimped on wire connectors. If you haven't found these connections this might be a place to check. Good Luck.
> 
> Robert


I saw that yesterday when I removed the thermostat from the wall. The wires are soldered to the thermostat, and then they have the crimp connectors from the wall wires to the thermostat wires. I checked all these connections and they all look fine.

At least the colour codes on the Coleman website match my colours. I still wrote down, took pictures, etc in case. Didnt cut anything else.

I have a Suburban furnace. Is there more than one blower fan on it. I could only see one at it moved freely. I dont think its a stuck blower fan however, because I think the fuse would last a little longer than it does while the fan tries to move. This is a snap of your fingers short


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## spidey

ob277rl said:


> Spidey I believe the thermostat only operates a relay in the furnace. If the fan was the problem it would blow a fuse on the furnace itself. The wiring for the A/C goes up the wall and into the ceiling and the separate wiring for the heater goes down the wall and through the under belly over to the heater location. I have opened up the belly of the beast before and the method of running wiring, plumbing, and heater ducts is chaotic at best. There is chance the wiring has been pinched or shorted out as a result of this. Now that you have identified the wiring at the thermostat try disconnecting them one at a time to see if the problem persists. Of course the hot and ground wires must stay in play to make this work. Start with the heater wire first then the A/C and then the fan wires. Good Luck.
> 
> Robert


So far I have the wires isolated to what is ac and what is furnace. Same colours that leave the thermostat are at the furnace. And then both go into blue wires seperatly.

If its not the thermostat, then it has to be a pinched wire. Especially when I tested it this spring all was well, ten suddenly this summer it started this..

The fuse will not blow unless the furnace is put on. In fact, the temp can be at the lowest and it happens. So the furnace isn't even getting the signal yet to say, turn me on. And everytime I test, it costs me almost $4 since the fuses arent cheap.

I was hoping after taking off the jack knife sofa that I would of just found a rubbed bare wire, just to make it easy


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## spidey

Does anyone know if the furnace board itself has a fuse on it. Read in a few places it might. Im still troubleshooting this thing


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## spidey

Well Im admitting defeat. I have wasted enough hours and have gotten nowhere. I have narrowed it down to when it calls for heat is when the fuse blows, I think. I had the temp to the lowest and turned it to furnace, and all was fine. I slowly slid the temp slide to warmer and when it got to needing heat, pop there goes the fuse.

I also was able to turn the manual on/off toggle switch off at the furnace, and when I put the thermostat up for heat, the fuse does not blow. So does that narrow it down to something on the furnace itself? Otherwise if it was the thermostat itself it would blow either way.

I don't know enough about this, and even though I have a multimetre, I don't know how to test for resistance correctly, or what readings are supposed to show up. And I cant get to the furnace well enough to check any wires without removing it, and Im not comfortable doing that.

Thanks for the help everyone, first time I will ever have to take a trailer in for repairs. Im totally stumped


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## spidey

Well there goes $600. Board on the furnace is gone, $160. So thats not bad. But they need to pull a brand new wire from the furnance to the thermostat as it is shorting out.

I have a progressive Industries surge guard, thought these things were supposed to stop this sort of stuff.

Another reason I want to get out of camping. Im sick of all these god damn repairs and now this bill.


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## spidey

Well, the mystery is solved, at a tune of $550. A staple in the roof perforated one of the wires. And over time rubbed bare and then shorted. The majority of the cost was labour of fishing the wire.

So I feel a bit better that it wasnt something I really could fix on my own. But I am sending a letter to Keystone. More and more I read on trailer manufacturing and quality control, seems this is an issue I shouldnt have to deal with


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## Leedek

Wow Spidey, perfect example of Murphy's Law. A staple prong... dang that is insane. Glad it's finally fixed.

Leigh


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## spidey

Leedek said:


> Wow Spidey, perfect example of Murphy's Law. A staple prong... dang that is insane. Glad it's finally fixed.
> 
> Leigh


3 hours labour, that was the expensive part at $120 an hour. That was including replacing the board as well.

They saved some time by going through the underbelly instead of the roof, since that would of involved removing panels. So they went under and up. If it wasnt a covered underbelly Im sure they wouldnt of been able to do that.

The staple went right through the middle of the two wires, so over time, it rubbed bare.


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## clark261

When none of the troubleshooting tips can solve the problem, the culprit is probably the wiring. Seek the services of a professional to test the wiring of your RV thermostat.


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