Amps Required For Suburban NT30SP - interesting problem

[66replica]

Hello,

I recently installed a NT30sp. I'm currently trying to hook up the 12V circuit but having a bit of difficulty. When hooked up to my trailer's 12V circuits, the blower motor does not kick on and the firing sequence does not start. However, when I hook up to a 12v 50amp battery charger, it kicks on and the start procedure works perfectly. I know I have old batteries and an old Univolt. They'll be replaced soon. Could I not be getting enough amperage? Ideas welcome.

[TG Twinkie]

Where are you connecting the charger? To the battery?
Are you sure the Univolt is working?
If you are connecting the charger to the battery cables and it works. That pretty much eliminates any bad connections, fuses etc.
have you checked the voltage coming out of the Univolt?
Voltage at the battery?
Do the lights work in the coach when you are on shore power? Do they go out or dim when you try to run the furnace?


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[66replica]

Great questions!

The Univolt works. My Fantastic Fans and LED lights all work great.

I'm connecting the 12v 55amp direct to the furnace.

When the trailer 12v system is plugged in, I get 13+ volts at the red 12v wire and the two blue thermostat wires as expected. I also confirmed my furnace ground is good (continuity between ground wire and ground on trailer body).

[TG Twinkie]

I would suggest you check to make sure the fuses are good and they are tight in the holders.
Old fuses can smolder internally. Which means that all that is left connecting fuse element to the cap is a carbon trail. In these circumstances you will read voltage with the meter because it is high impedance and doesn't draw much current.
Make sure the fuse holders are tight to the main buss and that they are tight on the wire terminal.
I would replace all of the old fuses in the Univolt with new fuses. Making sure the connections are tight. Then connect the charger to the battery and check for voltage.
It sounds to me like there is a problem with the circuit feeding the power to the furnace. It could be a simple matter of a bad connection.


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[idroba]

Measure the voltage at the furnace under load, that is when it is trying to run. If it drops lower than about 11 volts, it will not fire properly. Measure the voltage at the hot and ground wire as they come into the furnace, no where else.

I suspect you have a bad connection somewhere, or a bad fuse or ground. You could have some issues with the battery or univolt, but probably it is somewhere else.

When I re did my Argosy, I ran a new #12 wire hot and negative lines directly from the fuse panel to the furnace and another set to the water pump. I put each on their own fuse too. That made a world of difference with both of them

[66replica]

My converter was the issue. Once that was fixed, the furnace kicked on as expected.