Furnace problems again - Event Date: 26 Jun 2013 - 26 Jul 2013

I posted my previous problem with my furnace problem. Furnace ran on 12 volt, but not on 110. My RV dealer replaced the thermostat. I checked it at the shop on 110 before I pulled it home (100 miles away). I was camping in some high mountain areas this week-end (38 degrees at night with no shore power available). I tried the furnace on 12 volt and no "click, click, click", no fan, no nothing. When I got home I checked it on 110 shore power and it worked fine, checked on 12 volt and again nothing. I called the shop today and was basically told that my problem was impossible. Insinuation - I must be crazy. This is far from my first RV and know a little about running the things. Battery shows full power on the monitor panel, gas in the tanks, etc. Refrig works on 12 volt, H2O heater works on gas, lights work nice and bright, water pump works on 12 volt. Basically everything with any battery power works EXCEPT for the furnace.
Any ideas out there as to what may be wrong?
Not much confidence in my service tech.
Thanks for any help!!!

Camping was great, kayaking super, fishing great (catching not so good

I suspect that this isn't a furnace problem, rather a problem at your converter, or a battery problem.

A few things I'd check:
- multimeter on resting battery: voltage. On a charged battery, this should be between 12 and 13 volts
- multimeter across thermostat wires - again, this she be slightly above 12 volts
- with your r-pod connected to your vehicle and vehicle running, does the furnace work?
- move the furnace wiring to a new slot on the converter and use a new fuse.

Alternatively, as a long shot, it could be a resettable fuse on the furnace. Try disconnecting the negative lead on the trailers battery, leave for 30 minutes and then reconnect. Then try the furnace again.

But, my gut feel is low voltage... check the testing voltage, make sure everything else is off (fridge particularly) and try the furnace again.

Just found an interesting problem with my battery system.  I was having problems with my furnace in the past, and I just found that my battery disconnect switch is dropping 0.68V at 12 amps.  That may not seem like a lot but it's the same as if I had 20 feet of 14AWG wire in there.  That's enough to cause the furnace to fail firing up.  

I found that at the main ground buss (where all the ground wires are tightened down with screws)
that the main ground wire hooked to the chassis was almost loose. The screw holding it down
was a full turn loose. This would cause a voltage drop. Also the ground wire from the battery that attaches to the frame(left forward underneath) as well as the ground near the back from the frame
to the ground buss had a big voltage drop. The factory did not scrape away the paint where these grounds are attached but rather rely on the surface area of the screws as a contact area. This will allow low amperage without a voltage drop but a higher amperage will cause the voltage drop
to possibly not allow your heater to work. Also the main forward positive connector underneath the
trailer and exposed to the elements had lots of green corrosion. That was on my trailer that lives in
dry Idaho.