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Old 09-21-2019, 11:16 PM   #1
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Suburban furnace wont run on shore power or battery. Starts normal w/ generator 3500

Thank you in advanced for any and all help you may give. I've read through about 8 posts involving the suburban furnace =D.

2006 Eclipse Attitude 33AKS
33 ft toy hauler
SF-30F Furnace by Suburban
2- 7 gallon propane tanks
50 amp with 30 amp converter to 15 amp house plug. Plugged into a 15 amp regular house plug with nothing else on the circuit


Furnace will only light (DSI) with the Onan quiet 3500 generator running and ONLY IF--I unplug the shore power cable, then run the genator. In that order!!

I have NOTHING else plugged into the toy haulers electrical plugs when I try to do this....

Batteries are fresh. But how could this have anything to do with the batteries

I REMOVE the shore power cable 15am-30am-50 amp plug from the side of the toy hauler, start the genator, put back on "heat" then "high auto" then slide the temperature control to 90 and it fires and works no problem

Batteries are new, no volts tested but?? It only runs with the generator on ALONE. No shore power connected????? I understand it might not be getting the correct volts but ???

2nd problem: It also only lights with the main metal cover door unscrewed and sitting half way opened.

lol thanks for all your help and insight again!!

I imagine I am not getting enough volts somehow through the shore power?????

I plugged into a 2nd circuit on the house *15 amp but with ground fault breaker from a bathroom* also nothing else on the circuit.. Same issues..
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Old 09-22-2019, 05:02 AM   #2
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Problem 2 points to maybe the dsi grounding to the cover.

Problem 1 might point to converter....but not sure.
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Old 09-22-2019, 07:34 AM   #3
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Store bought adaptors or home made.

The 30 to 50 adaptor needs to connect the single incoming line from the house to both L1 and L2 lines of the 50 amp RV cord.

If not, you are only powering 1/2 of the trailer circuit breaker panel. See if other stuff doesn't work.

Next, the battery switch may be off or you have a dead battery. Could be due to a bad adaptor not sending power to the converter.

When you start the generator, the auto transfer switch switches to generator and powers both L1 and L2. That's how auto transfer switchs work, they have priority over shore power.

When the generator runs, the converter runs, powering the 12 volt system and charges the battery. That's what the heater uses.

GFCIs trip on many RVs. Seperate issue, unless that door you speak of is causing the 120 volt ground and neutral touch.
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Old 09-22-2019, 11:03 AM   #4
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1stt: thank you for your response.

How would one check to see if the lid is grounding to neutral? I thought maybe it wasn’t flipping the sail switch all the way, because of an imperfect bend in the 4 inch ducting? One of the bends off of the furnace cuts pretty sharply and maybe blocks 40% of that register.

Twinboat: they are store bought connector adapters. Is there a difference between a 50 amp direct to 15 amp adapter? It’s a 50 amp 4 plug to 30 amp 3 plug to standard house plug. 2 adapters between the main rv cable to my heavy duty house extension cable.

Good points my friend. Though the battery switch is on. Couldn’t I verify if the batteries are functioning by removing them from the equation? I turn the battery shut off to off for both batteries, plug into shore power... and the furnace still acts the same??

Everything does work. Every outlet, every device. Except the roof top ac triggers the house beaker as I assume it would.


Last night to get a couple hours of heat in the TH, I unplugged from shore power, started Onan quiet 3500 , turned furnace on. Turned on first or second spark of dsi (kept thermostat at 90 degrees) then turned off the generator and it stayed running. Plugged back into shore power and it stayed on for 4 hours before I cut it off.

Thank you for your help
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Old 09-22-2019, 11:12 AM   #5
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1st off......
Suburban SF-30F furnace runs on 12VDC POWER....and propane
RV Battery should be able to power the furnace W/O any AC Power source (Shore or gen)

Shore or Gen should supply AC to Converter which supplies DC System and charges battery
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Old 09-22-2019, 11:53 AM   #6
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Thanks biscuit.. Maybe I’ll go disconnect the cable and run furnace without the generator??

I think the culprit is the 50 amp- 30 amp paired with a secondary 30 amp- 15 amp connector. I’m not sure it likes the merriment.

With my very little understanding: is that the 50 amp plug requires two “legs” of power to properly power it. Could my adapters be screwing with the power?
Also why doesn’t only half the trailer work like another poster mentioned?

Going to go try running furnace on battery only ( and obviously propane) Maybe the generator wasn’t necessary at all.

I will try to get a direct 50 amp female to 15 amp male connector today
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Old 09-22-2019, 12:12 PM   #7
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Update

Sure enough. Generator was irrelevant. Unplugged from shore power, turned furnace on. Wouldn’t start first cycle. Removed Front furnace cover (two screws) , left sitting there half way. And it fires up like a champion....

Photo of door. And the adapters used off of main line
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Old 09-22-2019, 12:16 PM   #8
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Thinking out loud here. I’m thinking the cabling is the culprit of not having enough amps from shore power connection to open the gas line....

Problem number two has got to be the sail switch? It doesn’t like the amount of flow with the door attached. So I’ll try to fix that bend in the tubing to improve flow through the unit.
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Old 09-22-2019, 05:57 PM   #9
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Quote:
Originally Posted by Greshor View Post
Thinking out loud here. I’m thinking the cabling is the culprit of not having enough amps from shore power connection to open the gas line....

Problem number two has got to be the sail switch? It doesn’t like the amount of flow with the door attached. So I’ll try to fix that bend in the tubing to improve flow through the unit.

Once again......
AC has NOTHING to do with furnace operation.
DC Voltage operates Furnace FAN/Propane System from battery or via DC Dist from converter'


Furnace is a DC Hog and can drain battery easily.....but AC power to converter should charge/maintain battery voltage---even using a 15A outlet with adapters.
50A has 2 hots, 1 neutral and 1 ground......30A adapter has just 1 hot which is jumpered to supply both Hots in the 50A cord.....15A adapter is same as 30A just lower AMP so total AC amp draw is limited to 15A outlet.




Sail Switch 'paddle' is moved by the Fan wheel airflow.
Return air from inside RV goes thru the openings in the top/side of furnace cabinet. Rear access panel has nothing to do with return airflow

I think your problem is the access cover is shorting out the LIMIT Switch (Blue/White Wires)
Cover should NOT make contact with it when in place. Bend it inward OR install 'stand-offs' behind each cover screw.
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Old 09-22-2019, 06:52 PM   #10
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Okay thank you! Possible converter problem? Any thoughts?

Also old-biscuit: the only access panel is on the inside of the RV. Is that that the front or rear access? Also what is it exactly you are saying with those facts; considering my assumptions? Ty
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Old 09-22-2019, 07:50 PM   #11
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as mentioned the furnace should run on the 12 volt battery only. no ac power is required to run it.

look at your picture of the shore power cord and adapters. it looks like the black insulation has been pulled away from the 50 amp plug. i can see the individual current carrying wires inside. this is just a guess but perhaps that plug has an internal failure that is affecting the current flow. at the minimum test your shore power cord for connectivity. replace it with a new plug if necessary. you should wrap it with tape if you keep it. again only a guess.

also, stop worrying about not getting enough amps. 50, 30, and 15 amp circuits all supply 120 volt ac power. with nothing running the amount of amps the circuit can supply is not a factor. it is if you start high amperage devices such as the a/c.
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Old 09-23-2019, 05:58 AM   #12
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Okay thank you. Should have a new cable setup tomorrow. I can bypass the 50 amp black cable entirely.

The other way I am getting the furnace to fire up is by bypassing the converter. Flipping the converter breaker inside the trailer allows the furnace to fire right up. It does seem that with the converter OFF, the furnace fan is slowed down by about 10%. This is probably normal but of note.

Trying new cable setup tomorrow. Back to the converter being the problem me thinks. And next fixing why it only runs with the door off the front.
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Old 09-23-2019, 06:45 AM   #13
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You need a voltage meter, and start testing voltage at various locations. Without know what voltage is coming from the converter, batteries, and at the furnace, you are working blind. Unplug from shore power. Wait half hour and test house batteries. Voltage should be around 12.7 or so volts. Plug in the camper with converter on. Check at batteries for voltage, the should be slightly higher. If you have at least mid 12s, check voltage at furnace. The controls are 12 volt. Without the proper voltage, the furnace will not work. Possibly the converter is shot, but you may also have dead batteries as well. You shouldn't need to have shore power at all if your batteries are at a decent rate of charge. My two six volt batteries will run my furnace almost two nights here in Ontario.
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Old 09-23-2019, 01:00 PM   #14
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Will do. Appreciate you for the input Winniman
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