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Old 10-01-2017, 11:22 PM   #1
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1986 32' Excella
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Suburban Furnace Problem

I have an '86 32' Excella where I installed a new furnace, a Suburban NT-30SP. I put in a new unit, then warranty replaced a new circuit board, and now am on another entirely new unit. The same thing keeps happening to it: install, turn on the 'on' switch on the right side by the wiring harness, turn on gas, set temp at thermostat and the furnace blows and fires and turns off when the temperature is met. However after approximately 30-45 seconds after shutting down, the furnace makes an audible click and won't blow, turn over or reignite. I bypassed the thermostat and crossed and didn't have any power. I then turned the furnace switch off and then on again and waited without turning the heat on and the furnace clicks on when switched on but then clicks and turns off again after 30-45 seconds. Every time the furnace clicks and turns off there is no power to the thermostat on the wall at the back of the trailer. On a side note, the only electrical I have touched or replaced is the converter; I installed a new BD 1260C Boondocker BD1260C (60 Amp 4-Stage Converter/Charger). Any thoughts on what is going on? Circuit Board? Fuse?

Thanks,

Charlie
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Old 10-02-2017, 05:22 PM   #2
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* I bypassed the thermostat and crossed the blue wires and didn't have any power. *
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Old 10-03-2017, 04:59 PM   #3
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Sounds like a high temperature limit switch. If so it will need to be manually reset.
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Old 10-03-2017, 06:44 PM   #4
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- what do you mean by manually reset? Replace the switch? Or adjust the limit on it? I didn't think those switched were adjustable.
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Old 10-23-2017, 05:28 PM   #5
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Could the furnace be getting too much AC voltage that is forcing the furnace to shut off? I believe the furnace checks out and runs properly on DC only. What should the amps be to the furnace, if any at all? I'm getting proper DC but am also reading 31.9 amps at the furnace, 30.5A at the water pump in the back and 31.7A at DC wall outlet up front.
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Old 10-23-2017, 09:33 PM   #6
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The wiring to the furnace will not handle 30+ amps.
How are you measuring the current? Most VOM's will not read current in that high range.

What is the voltage?
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Old 10-23-2017, 09:50 PM   #7
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Your furnace should only run on 12 volt DC power. Heat is provided by the propane, and electric is used only to ignite, operate the electronics, and run the fan. Read the instructions that came with the unit for wiring. Suburban also has a good website. Good Luck
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Old 10-24-2017, 08:40 AM   #8
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I had an RV tech with me and we were using his multimeter.

12.9V to 12.2V when starting up.
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Old 10-24-2017, 08:47 AM   #9
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I know it should but I don't think it is. That's the problem. Suburban does not support retail customers, only service centers, and nowhere in their manuals do they list if the furnace has an amp limit or threshold. I believe the furnace is sensitive to too much amps but cannot confirm what the limit is. When disconnected from shore power and running on DC only it is perfect. When connected to shore power, something is throwing it off and shutting the furnace down. I replaced the old Univolt with a 60A converter/charger and am thinking maybe that is too much for the trailer. Should I be able to measure any amps on the DC wire?
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Old 10-24-2017, 10:10 AM   #10
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The furnace should not draw more than 10 amps. In fact it is probably less than that.
You can not force more amps. You can however force more voltage.
I think you have a problem with the newly installed converter.
You say the furnace works on battery power. But not when you are connected to shore power.
Do you have 120 volts on shore power?
What is the voltage at the fuse panel when on shore power?
What is the voltage at the furnace when on shore power?
The furnace may not be operating because of low voltage.
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Old 10-24-2017, 10:23 AM   #11
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Quote:
Originally Posted by LawsAirEx View Post
Could the furnace be getting too much AC voltage that is forcing the furnace to shut off? I believe the furnace checks out and runs properly on DC only. What should the amps be to the furnace, if any at all? I'm getting proper DC but am also reading 31.9 amps at the furnace, 30.5A at the water pump in the back and 31.7A at DC wall outlet up front.
How did you measure amps? Amps are measured in series with ONE appliance lead. No way water pump was drawing 30 amps. You can't measure amps at an outlet.

Al
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Old 10-24-2017, 10:45 AM   #12
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Quote:
Originally Posted by LawsAirEx View Post
Could the furnace be getting too much AC voltage that is forcing the furnace to shut off? I believe the furnace checks out and runs properly on DC only. What should the amps be to the furnace, if any at all? I'm getting proper DC but am also reading 31.9 amps at the furnace, 30.5A at the water pump in the back and 31.7A at DC wall outlet up front.
You shouldn't have any AC current at the furnace or any other of your 12v devices. Something isn't making sense here. How are you measuring amperage at the furnace, water pump, and D.C. Wall outlet? You should have 0 or nearly 0
Amps on a device that's not being used or in the off position. Right?
One of the blue wires going to the thermostat should always read 12v to ground. Doesn't matter which one. Those two blue wires are just a switch leg going to the thermostat. (Which is a switch) the red wire from the furnace harness is +12v and the yellow is ground or -12v. That's it, no cross over to any AC current. Have you measured the current between the yellow wire and a ground when the rig is plugged into shore power? It should be somewhere around 12.8 to 13+ volts DC.

Are you having problems with any other 12V device when plugged into shore power? This is sounding like something is miss wired or a converter issue or both. Did the problem start after you replaced the converter?

Once again, how are you measuring amps at the three places you mention? There shouldn't be any single device measuring anywhere near 30amps. The amp rating for your converter refers to total load of your 12v devices, all added together. My converter is rated at 45amps. So it can handle up to 45amps total load, many many 12v devices would need to be used at the same time to come near that total load. The nt30sp draws under 6amps.
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Old 10-24-2017, 10:52 AM   #13
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From vintage trailer supply:
"NT-30SP requires a minimum of 36 square inches of duct coming off the furnace.
NT-34SP and NT40 require a minimum of 48 square inches coming off the furnace.
When you receive the NT-30SP you will see that 3 of the 4 round ducts are open and the bottom rectangular duct is closed. This is the minimum ducting required. Or you can close the round ducts and duct solely from the bottom rectangular duct.
When you receive the NT-34SP or NT40, you will see that all 4 of the round ducts are open and the bottom is closed. This is the minimum ducting required. Or you can close the sides and use the bottom rectangle.
Don't forget to buy the accessories necessary to do proper ducting. Round duct covers, round duct collars, and the bottom rectangle duct adapter are sold separately."

Does your installation meet the 36 sq. In. requirement?

Al
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Old 10-24-2017, 07:38 PM   #14
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Thank you for the feedback. Yes I believe the furnace is installed according to the clearance limits and meets the minimum 36 sq in requirement. I was mistaken on the readings. The readings are AC voltage on the DC lines. The DC voltage at the furnace is 13.2 and 12.8 when running. The AC voltage is 31.9 at the furnace, 30.5 at the water pump in the back and 31.7 at DC wall outlet up front. Is that too much AC voltage? If the AC voltage seems right then maybe it is that the furnace on/off switch is faulty. Next step is to bypass the on/off switch?
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