I have a coleman evcon furnace. It will start with a 30 second purge but then go out. Sometimes it works just fine. What's my problem?

It could be many different items. Does the ignitor glow? What are the number of blinks on the circuit board and what does that tell you when you look at the code list on the back of the blower access door or on the drawing located somewhere on the furnace.

Coleman has made 2,127 different furnaces over the years so it is all guess work from here with the info you have provided.

Is this in a mobile home. If so then that makes a difference also.

The red light blinks once. This is in a house. model #BGM07516B serial #980905038. Hope this helps.

The red light blinks once. This is in a house. model #BGM07516B serial #980905038. Hope this helps.

Inside the furnace does the ignitor glow when it first comes on?

If it does but will not keep running it is possible the sensor needs to be cleaned. This is the cheapest item to try first.

One blink means ignition failure which could also mean the ignitor that glows could be defective also.

Picture of flame sensor LEFT

Then the hot surface ignitor.RIGHT

The pictures are what the items look like in general and do not represent exactly what the parts for your furnace will look like.