Model #DGAT070BDD COLEMAN EVCON Furnaces repair hemp

[1979CWB]

Hello, I'm helping I'm trying to help a friend fix a Coleman natural gas furnace. The furnace comes on and the igniter glows and the gas ignites. The blower blows and I can see flames through the small window. In this window I can watch the flames and the flame sensing rod. What I notice is the furnace runs very short amounts of time couple minutes at the most. But every time it shuts off it seems it' becase the flame is off the flame sensor for a couple seconds. The flames are a blue color inside the window but it seems the blower motor moves the flames and causes them to not always be on the sensor.  I' stumped and not sure if this is a gas problem a sensor problem or maybe even air flow problem? It seems to me if the flame sensor would stay in the flame the furnace may keep running. I' looking for any advice to push me in the right direction.  Thank you! 

[A & G Enterprises]

when the blower goes on you should not see the flames movement if you do you my have a cracked heat exchanger or flame rod migth be too short or not in right place

first try cleaning the flame rod with fine sandpaper

[1979CWB]

Thank you A & G Enterprises! i did notice this furnace has a recall for the heat exchanger i believe. I will look into this. I did notis that there does almost seem to be a breeze inside the furnace blowing around the flames.