Coleman gas furnace Model 7665-856, about 25 years old. Regulator and thermalcoupling and thermostat all replaced within last two or three years. Problem appears same as "THISAWAY" asked about 11/25/06. Furnace blows for about 45 seconds then shuts off. Burner appears to stay on when blower stops. Blower will come on after five minutes or so but continues to shut off after 45 seconds.

The fan motor is controlled by a fan switch that is activated by heat or by a time delay. Your sounds like it is a Heat controlled switch by the way it is working. So what needs to be done is some adjusting on the fan switch or to replace it all together. The fan on Temp should be around 135-140 Degrees F. The fan off temp should be at 95 F. The fan switch, if it is heat operated, is located on the inside wall of the furnace, just about 12 inches above the burners.

This is just a guess based on the information that you supplied in your question.

I'll look for a switch. I haven't seen one previously, but I'll look again. It sounds logical.
Condor 43

Called out the furnace man today. Problem was the burner wasn't getting hot enough due to restricted gas pipe at regulator going to burner. Furnace man removed cob web. Furnace working good now. Cost $115. Worth it.

Condor 43