Yes, I tested with 1) AC power connected, 2) after stove has fire. Thank you for your advices.
My furnace is DD-17DSI as
http://www.caztech.com/glider/TruckCamper/FWC/grandby/furnace/DSCF9770.JPG
Does anyone have similar problem on the same model?
-caz
P.S. Sorry for late response. I was out of...