Atwood thermal cut-off issue

[DVGaylin]

This one has me baffled.
I had a spider web nest in the LP blow through tube causing a block. The thermal cut-off link blew as it should.
I cleared the obstruction and removed the thermal cut-off (prior to noting the way it was connected. It has female connectors at both ends; I know, I should have taken pics).
I replaced the thermal cut-off with a new one but it blows the main 15 amp fuse in the coach.
If I by-pass the thermal cut-off with a jumper; all is well, but as soon as I put in that thermal cut-off; the 15 amp fuse blows.
To complicate things, I am not completely sure of the correct way the thermal cut-off should be installed I've tried both ways (using jumpers).

[dedmiston]

Aaaaand we're done.

Thank you for your help, Doug.

[dougrainer]

DVGaylin wrote:
Wow Doug!
The Electrode is the load to the circuit and can easily cause a fuse to blow. I NEVER said there was a short. You did.
I have worked in electronics for 35 years. I do not confess to being an expert but I have seen some odd issues that could not be completely explained without the proper testing equipment. This was one of those. It was a "Best Guess". Except the fact that it is working. The control module may have an under lying issue but until it goes out completely I will except what I have. You should too and quit being so negative.

I am not being negative. The plain fact is, you may have 35 years, but I have 41 years. I TEST the Atwood Piezo's all the time(hundreds) with a long screwdriver the metal shaft is grounded and I remove the Electrode wire and get the 1/8 inch gap to the Piezo spade to see if the Piezo will spark. I also will ground the Piezo spade. NOTHING HAPPENS. YOU are the one that has asked for help. If you are so smart(35 years), then why did you come to a forum for help? I get people like you all the time. Engineers bring their RV in and tell me how all their smart engineer relatives and friends have tried to fix the problem with their RV and now they grace me with fixing it. If you are so smart why do you ask for help? The NEW style Atwood boards have a 2 amp mini atc fuse on the board. Atwood states that if you go larger than 2 amp, damage to the board will happen(like grounding the gas solenoid wires. I still maintain your problem is at the Tstat/ECO mounting, probably the springs. DUE to your specific model that the brown wire comes from the switch and NOT the circuit board. I also maintain that the reason the short goes away, is because when you fiddle with the brown and thermal, you are causing the tstat/ECO springs to shift slightly. Have you removed the black felt cover to verify the tstat and ECO are mounted correctly? I hope you come back when your fix is not the problem and you state that. Doug

[2_many_2]

DVGaylin wrote:
Wow Doug!
The Electrode is the load to the circuit and can easily cause a fuse to blow. I NEVER said there was a short. You did.
I have worked in electronics for 35 years. I do not confess to being an expert but I have seen some odd issues that could not be completely explained without the proper testing equipment. This was one of those. It was a "Best Guess". Except the fact that it is working. The control module may have an under lying issue but until it goes out completely I will except what I have. You should too and quit being so negative.

:E

[DVGaylin]

Wow Doug!
The Electrode is the load to the circuit and can easily cause a fuse to blow. I NEVER said there was a short. You did.
I have worked in electronics for 35 years. I do not confess to being an expert but I have seen some odd issues that could not be completely explained without the proper testing equipment. This was one of those. It was a "Best Guess". Except the fact that it is working. The control module may have an under lying issue but until it goes out completely I will except what I have. You should too and quit being so negative.

[dougrainer]

DVGaylin wrote:
Problem solved...
I replaced the Spark Electrode. No more blown fuses.
The old Electrode must have been drawing just enough current to blow the fuse with the Thermal Cut-off in but not when the jumper was in. Weird...

BTW dougrainer, you forgot one thing; using a jumper did not cause the fuse to blow. So if there was a short somewhere the jumper would have blown the fuse as well. Thanks for replying...

There is more to this. NO WAY a Spark Electrode could cause a direct short to blow a 12 volt 15 amp fuse. Please come back when the short returns. Doug

[DVGaylin]

Problem solved...
I replaced the Spark Electrode. No more blown fuses.
The old Electrode must have been drawing just enough current to blow the fuse with the Thermal Cut-off in but not when the jumper was in. Weird...

BTW dougrainer, you forgot one thing; using a jumper did not cause the fuse to blow. So if there was a short somewhere the jumper would have blown the fuse as well. Thanks for replying...

[dougrainer]

The Thermal Cut off CANNOT cause a short to ground at all. IMPOSSIBLE!
It is isolated in the circuit and does NOT touch anything. So, that means I would BYPASS the 2 brown wires on the tstat and connect together with the Thermal installed. IF the fuse does NOT blow, your tstat is shorted to the aluminum tank. OR the 2 spades on the tstat are shorted in the tstat mount to the tank-----the spring for the tstat is not installed correctly. Have you pulled the black cover over the ECO and Tstat? If the fuse does blow with the tstat bypassed, then the Circuit Board would be the culprit. You may have stated but I missed it. Does the fuse blow immediately or ONLY when you start the ignition sequence? Doug

[Old-Biscuit]

DVGaylin wrote:
I do appreciate your input.
I could not see in the pic you posted which direction the tapered down side is pointing. The BRN wire or the T-stat?
Sorry, I should have said what model I have. My Atwood is a GH6-7E (Gas/Heat exchange with electronic spark). The 12 vdc comes from the switch in the coach, thru the Thermal Cut-off link, thru the T-stat and THEN to the Control BRD. If all safeties are met then the gas is turned on and the spark applied. A little different from the Electric/Gas model.

I literally removed the Thermal Cut-off link and used a wire with clips to connect the BRN wire to the T-stat. If there was a short in the BRN wire it would continue to short even with the jumper in place. I know it doesn't make since that the 15 amp fuse only blows when the Thermal Cut-off is used.

At this point I am thinking the Spark Electrode is causing some kind of load on the circuit when the Thermal Cut-off link is in and blowing the 15 amp fuse. I have a new Electrode coming tomorrow. We'll see...

OK--thanks for the Model Number but DC circuit is same...switch to thermal fuse to t-stat to board.
You state 15A fuse is blowing when thermal fuse is installed....implying thermal fuse was at issue

Now you are talking about Spark electrode.
Does the 15A Fuse BLOW when the Spark Electrode and Gas Valve DC is in ignition phase??

As for thermal fuse connection......
Clear wire/bent end connects to t-stat
Thermal Device is at other end connected to Brown wire so that IT is exposed to Excessive HEAT from blowback

[DVGaylin]

I do appreciate your input.
I could not see in the pic you posted which direction the tapered down side is pointing. The BRN wire or the T-stat?
Sorry, I should have said what model I have. My Atwood is a GH6-7E (Gas/Heat exchange with electronic spark). The 12 vdc comes from the switch in the coach, thru the Thermal Cut-off link, thru the T-stat and THEN to the Control BRD. If all safeties are met then the gas is turned on and the spark applied. A little different from the Electric/Gas model.

I literally removed the Thermal Cut-off link and used a wire with clips to connect the BRN wire to the T-stat. If there was a short in the BRN wire it would continue to short even with the jumper in place. I know it doesn't make since that the 15 amp fuse only blows when the Thermal Cut-off is used.

At this point I am thinking the Spark Electrode is causing some kind of load on the circuit when the Thermal Cut-off link is in and blowing the 15 amp fuse. I have a new Electrode coming tomorrow. We'll see...

[Old-Biscuit]

DVGaylin wrote:
Thanks for the reply.
I agree completely. Fusible link...
I am doing what I call the "Spock" method, BEST GUESS.
I am going to replace the most logical components and see if I get lucky.
I've ordered the Main Burner and the Spark Electrode.
I ordered the Main Burner because it is looking old and I just wanted better control over the air to gas mixture (nice blue flame with no noise).
I ordered the Spark Electrode because it is the end load that the control board controls and if it is pulling too much load? Best guess...
I'll try the Control Board next if the Electrode doesn't work but it is $100 - $150 so I am hoping it is the Electrode.
There really isn't anything else in the circuit.

In my first post IS a picture of thermal cut off INSTALLED........

As for all those parts....
thermal fuse is FIRST inline with the DC Circuit.
Look at wiring diagram ....DC from switch to circuit board then from circuit board to thermal cut off

NOTHING else gets DC until it goes thru the thermal fuse/thru t-stat and back to circuit board
Spark Electrode is LAST thing in the DC Circuit (along with the DC to Gas Valve---both get DC at same time)

15A Fuse blowing with thermal fuse in place BUT not blowing when thermal fuse bypassed suggest short/bad wiring (Brown wires)

When you say 'jumpers' are you using actual extra wires OR just removing thermal fuse and connecting brown wire from circuit board directly to t-stat??????

[DVGaylin]

Thanks for the reply.
I agree completely. Fusible link...
I am doing what I call the "Spock" method, BEST GUESS.
I am going to replace the most logical components and see if I get lucky.
I've ordered the Main Burner and the Spark Electrode.
I ordered the Main Burner because it is looking old and I just wanted better control over the air to gas mixture (nice blue flame with no noise).
I ordered the Spark Electrode because it is the end load that the control board controls and if it is pulling too much load? Best guess...
I'll try the Control Board next if the Electrode doesn't work but it is $100 - $150 so I am hoping it is the Electrode.
There really isn't anything else in the circuit.

[wa8yxm]

Unless the brown wire had insulation melted and the bare spot is touching something and when you move the wires to "Jumper" the Thermal cutoff it's either shorting or un-shorting I see not reason for the Fuse (for that's what it is) to cause the main fuse to blow.

IN "normal" operation it's a jumper wire. Just like the jumper wire you use to replace it.. Only time it is something else is if it gets too hot then it opens. Like a fuse. It's well Insulated by the plastic. Should not blow the fuse.

possible bad connection That can blow fuses by causing the device to "Stutter".

[DVGaylin]

Does anyone have a pic of the thermal cut-off link as it sets inline with the T-Stat? That would at least show me the correct way the link is supposed to be connected (if there is a correct way). It should just be a fusible link, open or closed, so the direction shouldn't make a difference.

[DVGaylin]

Thanks for the reply Old-Biscuit.
I believe the new thermal cut-off links are the same as the one I removed except the new ones have 1 female connector and 1 male connector (They also sent a brn wire with a female connector on it).

The biggest confusion is; if I bypass the thermal cut-off with a jumper - all is fine, but once I put the thermal cut-off link in I blow the 15 amp fuse. I put a meter on the new thermal cut-off link and it measures 0 on the ohm meter, the same if I use the diode test (I don't really think this thermal cut-off link is a diode even though it looks like one, I think it is a thermal fuse. It doesn't limit the direction of the current but simply opens the connection if the temp gets too high). I got 3 thermal cut-off links and all read the same way. No resistance is the same as if I put a wire (jumper) in it's place. So why would I be pulling > 15 amps with the thermal cut-off link as compared to just using the jumper? They both show 0 resistance on the meter!
Thus the confusion.