Furnace/Fan won't run under 11.8 V

[cmerkert]

We just purchased a 2014 Cougar 31SQB. When boondocking, the furnace and blower would not run at night. It would actually run when initially turned on (12.6 V reading), but when up to temp thermostat kicks it off and it will not come back on when temp drops. This has happened several times. During the day I. Trials it works multiple times. Run generators for an hour to fully recharge the 2 brand new 12V batteries. Start the furnace and it works. Turn it off and an hour later it will not work. Minimum lights on for short time and a 12v tv for a little. Volt reading is under 12v and it will not work.

Does it really require a full 12v charge to run? If so, that does not allow for much living if need to conserve the full 12v.

Or

Are the batteries dropping down below 12v way too quickly. I would think 2 12v deep cycles in parallel would hold their charge longer. 1 hour of tv and one light would use up that much?

Later that night at 2am I fired up the quiet generator (no one near us) and got heat going. This recharged for 20-30 mins. But once the blower went off at temperature, it did not come back on again for the rest of the night. And this was a 50 degree spring night. Can't imagine in freezing temps.

Anyone have any insight.

[f6bits]

Sounds like my first boon docking trip. I had the one 12V battery my trailer came with. Sub-freezing temps and the furnace didn't last long. I had to run my generator most of the night to keep power to the furnace.

Now I run two 6V golf cart batteries without a problem.

p.s. my signature pic is from that very trip.

[JRTJH]

One hour of TV (depending on the type of TV and the size) could easily deplete the charge on a battery bank. The furnace is "sensitive" to the voltage input. There is a "sail switch" in the air distribution system and if the furnace fan isn't blowing hard enough to push the sail switch to close, the ignition sequence will not happen.

There are other issues that could be occurring, but you didn't say if the furnace operates "normally" when you're connected to shore power. If it does function normally when on shore power, then it's your 12 volt supply that's causing the problem.

Yes, two 12 volt deep cycle batteries, depending on the size and amperage rating, could easily be well below 12 VDC after an hour of TV viewing.

If your RV is still under warranty, you might want to discuss the problem with your dealer. There is a remote chance that the windings or brushes in your fan motor are drawing too much amperage and depleting the battery, but that's really an "outside" shot at trying to blame the furnace. Chances are your batteries just aren't strong enough to do what you're trying to do. Try running all night on shore power, if you can, then it's probably the batteries.