When the temps outside dip into the low 30's and you're boondocking w/out electric.
Atwood AFMD30111 - one light every three seconds means "air flow / high limit".
If it's air flow - then it's a new problem because this is season 2 and we used the furnace in March of this year.
No attempt at a spark/ignition.
The blower just runs for 20 seconds then shuts down.