I have a mobil home furnace coleman/evcon DGAT model
The purge blower comes on the ignitor comes on the flame comes on and after about 40 sec the blower comes on and the flame goes out.
This model does not have a pressure switch.
Need some help

I took apart the burner assy and cleaned the sensor with emery cloth but still won't work

The flame goes out just as the blower starts I checked the wires they seem to be tight
I checked the exchanger for crackes or burn spots with the burner out every thing looks OK
No headaches or stuffynoses

Sounds like you have a dirty flame sensor. It may be kind of a tricky to remove and clean it if you do not know the mechanics of a mobile home furnace.

You better have a look at this.

Safety/Inspection Notice (http://www.dgatprogram.com/)

There have been major problems with the heat exchangers. This can cause a pilot problem. Been there done that.

Thank you for your help.
I took apart the burner assy and cleaned the flame sensor with emery cloth but still the same should I replace the flame sensor
Thanks eric

If you have an ignitor, you don't have a pilot light so I doubt the second post applies. Although leaky heat exchangers kill.

Go to the top of the sticky and read the sequence of operations of a gas furnace. I think if the flame sensor is bad the gas goes off before the blower starts up. I think the control board isn't getting the signal that the blower started.

A hole in the heat exchanger will blow the flame away from the sensor. This inturn will cause the series of events you describe. When you said as soon as the blower comes on the furnace goes out!! This is a classic example of the Coleman problem. Headaches,stuffy nose,flue like symptoms Etc come usually before you pass out. Please have your heat exchanger checked. The repair is free from Coleman. These units were shipped from the factory over fired. The heat X will not take the BTU imput. They replace the heat X and underfire the unit with a different orifice. This problem can and will kill you without proper attention.