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Author Topic: Suburban furnace questions  (Read 4620 times)
clemlaw
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« on: October 10, 2009, 06:28:09 PM »

Due to a SPUT on my part today, I manage to fry our furnace.

The thermostat decided to stop working, so I removed it, planning to replace it (with one with no moving parts, if possible).  It is basically a simple switch that closes the contacts on two wires running to the furnace.  Since we didn't have a thermostat, I simply removed it and left the two exposed wires.  When we wanted the heater turned on, we just twisted them together, and it worked fine.

When we were getting ready to leave, for reasons that I won't go into, I grounded one of the wires to the door frame of the camper.  A very brief "squeak" sound was heard from the heater, and after that, the heater was no longer working (nothing happened when I twisted the wires together again).  So obviously, I let the smoke out of one of the components inside the furnace, and of course, the smoke inside is what causes electronic devices to work.

The schematic that is supplied with the furnace isn't very helpful, since it just shows the two thermostat wires going to something called the "module board".  This is a PC board apparently with a full name of "fan control module board".  It is identified as one part, and the instructions state that individual parts can't be repaired, only replaced.

The only glimmer of hope is that the schematic does show a single fuse for the furnace.

Here are my questions:

1.  Does anyone know where that fuse is located, or whether there is another fuse in there that's not shown on the diagram?  We were in a hurry to pack up and get home, and so far, I haven't really taken a look.

2.  Is replacing the "module board" something I can do myself?  If the board is readily accessible, I'm comfortable taking it out and putting in a new one.  In fact, if I had a schematic of the board itself (which I realize is probably not available), I could probably repair the damage.  However, I am not comfortable removing mechanical components in order to get at it.  I know my limitations, and if I have to unscrew too many pieces to get it it, I won't be able to put it back together (or after putting it back together, there will be the dreaded leftover parts). 

From the blow up diagram that came with it, it looks like it's in the middle, but I really can't tell.  Does anyone know if that's something I can get at without much difficulty?

The furnace is Suburban model DD-17DSI, and the "module board" is part # 520820.  It is part #32 on this diagram:

http://www.laurelhurstdistributors.com/parts/furnaces/Suburban_DD17DSI.html

For some reason, the fuse holder is not shown on the diagram.  To me, part #32 looks hopelessly buried on this picture, but maybe someone here can give me some moral support.   Cool
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cruising usa
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« Reply #1 on: October 10, 2009, 06:44:23 PM »

Don't know where the fuse is in the furnace. Could it possibly blown the fuse at the converter?  Good Luck
Ken
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rabird
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« Reply #2 on: October 10, 2009, 06:45:25 PM »

There are several things that happen before the board gets involved.
1st is the a relay
http://bryantrv.com/docs2/docs/suburbantech.pdf
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clemlaw
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« Reply #3 on: October 11, 2009, 08:09:54 PM »

Quote
There are several things that happen before the board gets involved.
1st is the a relay
http://bryantrv.com/docs2/docs/suburbantech.pdf

Thanks for posting that link!  At first, what it was saying there didn't match up with what I remembered on the wiring diagram.  But it turns out in my haste, I got mixed up and was following the wrong wire on the diagram.  When I took another look at the diagram, it turns out that the wire I shorted to ground was actually 12 volts straight from the converter.  Therefore, there's a pretty good chance that I blew the 4 amp fuse.

The location of the fuse is not shown on the diagram, which leads me to believe that it might be an inline fuse, so I can probably get it at just by feeling for the wires.

Quote
Don't know where the fuse is in the furnace. Could it possibly blown the fuse at the converter?  Good Luck

Thanks.  Chances are it's the furnace fuse, but the converter fuse is a lot easier to check, and it was a short circuit right across it, so that's where I'll check first!

Right now, it's too cold to go crawling around in there, but now I have some confidence that it might be an easy fix!

If anyone knows for sure where that fuse is, I'd appreciate it!  Also, assuming I get it fixed, what thermostat would you recommend?  I really don't need one that is particularly accurate, but the mechanical thermostat that was supplied with it just didn't hold up very well getting bounced around.  Do digital thermostats use some kind of electronic sensor to read the temperature?  If so, it seems like that would hold up a lot better.

Oh, and for future reference, it's not a good idea to touch the thermostat wires to the door frame.   
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clemlaw
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« Reply #4 on: October 15, 2009, 07:40:04 AM »

Thanks for getting me back on track.

It was indeed just the fuse, and the fuse was easy to get at.  In fact, if I had looked closer prior to packing up, it would have been visible right behind the grate.

I couldn't find any 4 amp fuses at home, but it started right up with a 3 amp fuse.  Now, I just have to make a trip to the hardware store to look at thermostats (and some spare fuses).

So it turns out it was just a minor SPUT after all.

Move on people; nothing more to see here.  Big Smile
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austinado16
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« Reply #5 on: October 15, 2009, 04:09:24 PM »

Man, did you luck out!!
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clemlaw
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« Reply #6 on: October 15, 2009, 06:50:39 PM »

I explained to my wife that she lucked out.

She didn't do anything to stop me when I decided to touch the wire to ground.  Fortunately, no harm was done, because I was able to fix it.  I did explain that she needs to be more careful next time.   Tongue
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austinado16
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« Reply #7 on: October 15, 2009, 09:15:09 PM »

Way to go man!  Always keep 'em guessing.
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