enblethen wrote:
Verify the voltage at the furnace when plugged in and when running on batteries.
Possible converter is failing.
YEP^^^^^^
When NOT plugged in your Trailer Battery is supplying the DC for Furnace operation
When plugged in the converter is supplying the DC for Furnace operation
And converter should be maintaining/charging trailer battery
Could be a capacitor is failing in the converter. Capacitors are used to 'filter' the converted AC to DC Power
Unfiltered DC can charge the battery but will cause issues with circuit boards
To check
Use Voltmeter set to AC Voltage
Then measure the DC System Voltage
If you get a reading over 6VAC on the DC then converter capacitor is/has failed
Otherwise...when plugged in Furnace should work better then when on battery alone