I can see the burner igniting and the gas burning. Then a few seconds later the blower kicks in but kicks out shortly after coming on. Switched thermistat to on position and blower does the same thing instead of coming on running continuously? Unit just will not run long enough to heat the house. It is a comfortmaker furnis. Could this be a relay for the motor or one of the limit switches acting up. Any info on what to check would be very helpful, thanks

Sounds like the fan control is defective allowing the blower not enough run time.

How do I check the fan control?

Does the fan motor feel hot? Careful, don't burn your fingers. If not, you will need a voltmeter to diagnose the problem.

I have a voltmeter I am just not sure what to check that would be controlling the motor, the motor does not stay running long enough to really get hot

Give us the brand and model # of the unit.

The name is Comfortmaker on the outside panel. The name on the inside of the unit is Snyder General. Model # GUG070A012N and serial # R900800203. I found a filter that was sucked into the return that was cuasing part of the cycling problem. It runs in he on position now but does not work in the auto position on the stat.

That is a ICP brand furnace.

This should be the part you need.
I would not buy the part there you can probably find it cheaper. This is just to give you a idea of what the part looks like. It is adjustable for a longer run time.

11" Fan & Limit Switch Honeywell (3 or 4 wire switch): Nationwide HVAC Parts (http://74.125.47.132/search?q=cache:ZiW7siG1lvQJ:www.nationwidehvacpart s.com/Merchant2/merchant.mvc%3FScreen%3DPROD%26Product_Code%3DFLT6 4B2210%26Category_Code%3Dhw-flc+GUG070A012N&hl=en&ct=clnk&cd=16&gl=us)