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Old 04-19-2013, 03:21 AM   #1
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Suburban Furnace blowing fuse for fridge

I have a Rockwood Signature Ultralite 5th Wheeler 8244WS. After 6 months of travelling I have a problem with the furnace blowing fuses which causes the fridge to stop working on Gas or 120W power. The furnace has worked fine for the last 2 weeks since it got cold here (Tasmania, Australia). I turned on the heater and it ran for about 3 seconds and then blew the fuse for the burner and fridge which seem to be on the same circuit.

After replacing the fuse 3 times on the 4th attempt it held OK and the fridge worked fine again. I left the furnace off for 2 days then this morning turned it on and it immediatel blew the fuse. I now have tried to replace the fuse about 5 times and each time it blows.

Is there any way to disconnect the furnace from the same circuit until I get it fixed. Then I can still use the fridge which is the most important appliance. I can live without the heating for now. I would appreciate if anyone knows how to disconnect the power from the furnace without dismantling it. There is no wiring diagram in the user manuals that show where the wires are to disconnect it.

Please help !!!
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Old 04-20-2013, 05:46 AM   #2
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You have a short somewhere in the furnace and it could be just about anywhere. It might be easier to move the fridge to a different fuse.

Push come to shove, you can tap directly off the 12 volt battery connection at the converter and (using a pigtail 10 amp fuse) home run a new one directly to the fridge.

As to the furnace, I would start my troubleshooting by disconnecting the furnace 12 volt wire connection and see if that stops blowing the fuse.

Then look at the wires in the furnace and the blower motor.
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Old 04-21-2013, 07:00 AM   #3
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Thanks for the quick response. Being a bit of a novice here - how do I disconnect the furnace 12v wire connection? I can only see some blue, red & white wires entering the furnace from the right side. The furnace is mounted under the fridge. I have been able to get the fridge going again after changing the fuse about 8 times. Each time I turned the 12v power on (after putting in a new fuse) I could hear the furnace blower start momentarily (about 2 secs). Eventually it stopped blowing the fuse. Now I am not game to turn the heating on again in case it blows the fuse again. The heating has been turned off now for a few days but the blower still tried to start each tiime I replaced the fuse. I also noticed that the same fuse runs the water heater. It does not seem to make sense having the furnace, refridgerator and water heater all on the same fuse.

Do I have to fully dismantle the furnace in order to get to the wires so I can disconnect it? I cant seem to find any on/off switch on the furnace itself.

regards
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Old 04-21-2013, 07:40 AM   #4
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Originally Posted by OZZIEROCKWOOD View Post
Thanks for the quick response. Being a bit of a novice here - how do I disconnect the furnace 12v wire connection? I can only see some blue, red & white wires entering the furnace from the right side. The furnace is mounted under the fridge. I have been able to get the fridge going again after changing the fuse about 8 times. Each time I turned the 12v power on (after putting in a new fuse) I could hear the furnace blower start momentarily (about 2 secs). Eventually it stopped blowing the fuse. Now I am not game to turn the heating on again in case it blows the fuse again. The heating has been turned off now for a few days but the blower still tried to start each tiime I replaced the fuse. I also noticed that the same fuse runs the water heater. It does not seem to make sense having the furnace, refridgerator and water heater all on the same fuse.

Do I have to fully dismantle the furnace in order to get to the wires so I can disconnect it? I cant seem to find any on/off switch on the furnace itself.

regards
Sounds like all three appliances share the 12 volt (not a good idea I agree) but they share because its only appliance control power they use, the bulk of the energy is gas. The heater sounds as though it may be shorting due to moisture. You struggle a few times to get it lit and then in sustains after warming. The other possibility is electronic component failure once warm with hold. If you can ID which lead carries the 12V+ to the heater using a meter you can cut it and lead a temp fused 12V+ from another source. Only a guess, the red is your man!
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Old 04-21-2013, 07:41 AM   #5
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Each time I turned the 12v power on (after putting in a new fuse) I could hear the furnace blower start momentarily (about 2 secs).


Ozzie turn the thermostat OFF and the blower should not try to start. If it still does; that is where your short is.


I also noticed that the same fuse runs the water heater. It does not seem to make sense having the furnace, refridgerator and water heater all on the same fuse.


The water heater draws very little DC power; just enough to basically open the gas valve; same with the fridge. The furnace is the power hog.


Do I have to fully dismantle the furnace in order to get to the wires so I can disconnect it?

Maybe. Since all the wires are in the same place and are connected together, they should join somewhere close. Look for that junction of RED wires (and with the fuse removed) take the junction apart and removed the red wire going to the furnace. Otherwise you will need to remove the access panel on the furnace.


I cant seem to find any on/off switch on the furnace itself.

There is no "ON/OFF" switch. Just the thermostat. (see above)
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Old 04-21-2013, 07:45 PM   #6
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herk7769 many thanks for your assistance. It is all starting to make sense now.

I originally struck the problem when I went to turn on the heater at the thermostat and it momentarily came on then went off and blew the fuse and subsequently stopped the fridge and water heater from operating.
I immediately turned off the heater at the thermostat and replaced the fuse. Each time I replaced the fuse I heard the furnace startup then immediately stop and in the process it blew the fuse again. I did this several times blowing about 10 fuses. It was strange that the furnace kept trying to turn on even though I had switched it off at the thermostat. I then left out the fuse and turned off the isolator to the main batteries and each time I turned it back on I heard the furnace try to start.
Now I am wondering if the furnace was still in "run down mode" and had not finished its sequence so after turning the battery isolator on and off several times it eventually reset or finished its close down sequence?

Now I have succesffully got the fridge and water heater working but reluctant to turn on the furnace again until I solve the problem.

Maybe I need to replace the thermostat ? The Rockwood is only just 12 months old so I was not expecting this problem.

Do you think I should go with the thermostat replacement or could it be a furnace problem? I have noticed many forum comments about furnace problems but not sure if mine is related.

many thanks again
John
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Old 04-21-2013, 08:07 PM   #7
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The thermostat is the cheapest item; BUT I doubt it would cause blown fuses.
I think you have an issue in the heater.

Having said that; it can't hurt.
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Old 04-21-2013, 10:15 PM   #8
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Quote:
Originally Posted by OZZIEROCKWOOD View Post
herk7769 many thanks for your assistance. It is all starting to make sense now.

I originally struck the problem when I went to turn on the heater at the thermostat and it momentarily came on then went off and blew the fuse and subsequently stopped the fridge and water heater from operating.
I immediately turned off the heater at the thermostat and replaced the fuse. Each time I replaced the fuse I heard the furnace startup then immediately stop and in the process it blew the fuse again. I did this several times blowing about 10 fuses. It was strange that the furnace kept trying to turn on even though I had switched it off at the thermostat. I then left out the fuse and turned off the isolator to the main batteries and each time I turned it back on I heard the furnace try to start.
Now I am wondering if the furnace was still in "run down mode" and had not finished its sequence so after turning the battery isolator on and off several times it eventually reset or finished its close down sequence?

Now I have succesffully got the fridge and water heater working but reluctant to turn on the furnace again until I solve the problem.

Maybe I need to replace the thermostat ? The Rockwood is only just 12 months old so I was not expecting this problem.

Do you think I should go with the thermostat replacement or could it be a furnace problem? I have noticed many forum comments about furnace problems but not sure if mine is related.

many thanks again
John
I just reviewed the schematic for the SF35 and others. Seems the 12VDC is fed to the circuit board 24/7. When the thermostat is on and signals go, a second 12 volt signal goes to the board. This allows the motor to start and only after it reaches 75% it allows the igniter and the gas valve. Since it is self starting and blowing fuses I'm agreeing with Herk but narrow it down to a defective circuit board. Seems the only device that can cause self start and shorting to ground. Not sure if less than two years, if so its warranty.
Here's a schematic near last page.
Attached Files
File Type: pdf Suburban Furnace SF-42.pdf (945.6 KB, 107 views)
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Old 04-23-2013, 12:09 AM   #9
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Blowing fuse for fridge

Many thanks for your replies HERK & VINCE.

I will endeavour to pull out the furnace and have someone test the circuit board as suggested. It makes sense that the problem is with the furnace itself. It would be good to have the furnace 12v power with its own fuse so I will investigate that also. I have a problem with warranty as I am in Australia and the 5th wheeler was imported here last year by a private individual. I have to send the furnace back to USA for warranty so I have to be 100% sure its the problem.

"life was not meant to be easy"

regards

john OZZIEROCKWOOD
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